Fonts
The manual uses Gotham (usually bold) for the sans serif titles and callouts, and Garamond for the main text. The example gameplay passages use GFY Thornesmith. Evil Hat have their own font for the Fate action glyphs.
Gotham is a priced font, but I hear Google's Montserrat is a good substitute and uses the SIL Open Font License. Garamond has priced variants (the manual uses Adobe's I think), but URW make a version called Garamond No. 8 — you can download a TrueType Garamond No. 8 from Github (under the AFPL). GFY Thornesmith is also priced, and I don't know of a good (free) visual substitute, but Blambot make a bunch of comic fonts that are free for personal use (eg. Heavy Mettle, Nightwatcher).
Style
As for replicating the style, all I can say is: pay close attention to the little visual cues we often take for granted. Note the 45° corners on the black callout boxes, and the drop shadow. Note the indent for, and horizontal lines above and below, the example text. Also there's frequent use of bolding to emphasise aspects and other mechanical details. In general, it's got a very high-contrast, solid black-and-white style. Compare it to, say, most WotC D&D material where everything is in subdued browns, reds and cream colours with a lot of texture.
There's a fair amount of artwork in there that breaks up the walls of text; if you can't make your own artwork, just do a Google image search (eg. I just searched for "[genre of game] vector artwork"). There's a lot of stuff that's free for personal use, but remember to respect the license if you publish it. I like to have it "enter the page" from the side or lower corners and wrap the text around it, you might prefer to feature it within the page proper. The manual uses artwork with a little bit of texture (which contrasts nicely with the heaviness of the text, and so doesn't really need captioning or framing); personally I find that solid vector based stuff works fine as well, as long as it's in moderation.
Structure
Finally, note that it's the structure of the book that dictates these elements. The text regularly switches between "main text," example gameplay, and helpful tips. Each of these elements has its own style. Putting random paragraphs in big white-on-black boxes, or switching to a hand-drawn-looking font for no particular reason will just be jarring. Text with the same font should be able to be pulled out by itself and still make sense (or at least give you a coherent set of excerpts).
Caveats
There's a lot of merit to trying to reproduce your system's look and feel; it can really help reduce cognitive load for your players switching between the official material (such as the manual) and your own handouts. Having said that, if you get close but not close enough, you can set off a bit of dissonance as your players' expectations are subtly missed in ways they can't quite identify.
I already mentioned this, but you said you were doing this for personal use but thinking about publishing your material later. Even if you're publishing it for free, it probably won't fall under "personal use" any more, and you'll need to be careful to respect the licenses of any fonts and artwork you use. This may simply mean captions for crediting images, or it may mean thinking about a real license.
When I do stuff like this, I like to keep a text file alongside my material with a list of anything I downloaded and used, along with source URL and a quick note about the license. (You'll also appreciate this when you render a PDF, accidentally delete your source file, and then wonder where you got that picture of a planet from.)
The OGL itself contains full instructions on using the OGL
Using the Open Gaming License requires following its instructions to the letter. That's the nature of a license: it tells you exactly and completely what you must do to use any material covered by it, and if it's not in the license, you don't have to do it to be in compliance with the license.
One of the OGL's own instructions covers your question. You must include a full copy of the license with your work that used the license:
- Copy of this License: You MUST include a copy of this License with every copy of the Open Game Content You Distribute.
(Of course, you are also required to update your copy of section 15, because that's part of following section 6. And section 8 does require you to indicate what is your product identity [if any], but you don't do that in the copy of the license, just somewhere in your product.)
Regarding length, be aware of what parts of the first two pages of the SRD are the OGL's text and which aren't: everything from “Permission to copy…” to “… The terms of the Open Gaming License Version 1.0a are as follows:” are not part of the OGL and need not be reproduced. Those are part of the SRD itself, and only introduces the OGL.
The OGL itself begins at “OPEN GAME LICENSE Version 1.0a”, ends at “END OF LICENSE”, and you have to copy those parts and everything in between. The font can be small, but it does have to be legible, since anyone using your own material needs to be able to read the license you are letting them use it under. (For an extreme example, the smallest legible size Legendary Games prints their OGL copies in is a 5-point font.)
Page count and font size is less of an issue if you put the OGL out of the reader's way, too. Most (all?) RPG books that use OGL-licensed content put the necessary copy at the end. The SRD is unusual in putting it in the front, simply due to the importance of the OGL to the basic nature of the SRD. You can safely put the OGL wherever you want, but as a publisher, putting it in the back of the book is often ideal — those who need to read it will know to look for it, and those who don't won't be bothered by a surprise block of legalese in their way.
Best Answer
Legal issues
First, I'm not a lawyer. I've spent the past 15 years paying attention to the shifting landscape of copyright and trademark and other IP law, so I can point you toward a few ideas that might help, but I'm still not a lawyer and can't give you legal advice that's worth a damn when you actually start publishing.
Infringing others' IP rights
There are a lot of myths about copyright floating around, and it has the predictable effect of freaking out new creators (ironically so, considering it's supposed to create certainty and calm). The important thing to know is that copyright can't be infringed unless you've copied (hence the name) from someone else. It's also important to know that in the United States and some other places, being innocent is no protection from being sued into oblivion by anyone who decides to, and frivolous lawsuits can be used by those with lots of money as weapons against those who can't afford to be sued: even if they would eventually be proven innocent, usually they're bankrupted long before the trial is over.
As a result, the person to talk to about copyright (and trademarks) is a lawyer, not us. Note that in the US, game mechanics can't be patented, so there's at least one bit of law that you don't need to worry about. Aside, you're unlikely to fall afoul of trademark law either, unless your games' titles or major technical terms closely resemble (or resemble when taken in aggregate) an existing game's title or terms.
All that aside, there are thousands upon thousands of roleplaying games published, and hundreds upon hundreds more every year, and very few of those creators have bothered to retain a lawyer. The roleplaying games industry is actually pretty tiny as publishing industries go, and small players simply don't get into legal trouble by publishing a new game. The only people who generally have to worry about legalities are the people producing material designed to work with (or even clone) existing games, and it sounds like that's not your situation.
So really, read around a while about copyright and trademark, get that bit of education that's possible by reading up on Wikipedia and other relatively-reliable sources, and have a good think about whether what you're looking to publish is going to make any existing publisher unhappy. Likely the answer will be no, but by then you'll have a more confident grasp of the legalities and you'll be able to decide better when you need lawyer-shaped legal advice.
Protecting your own work
As for enforcing your own copyright, you're automatically protected if you're in the US, Canada, or the UK. (Possibly elsewhere too, but I'm not as familiar with copyright elsewhere.) Copyrights don't need to be registered anymore in order to be protected. If you do find that others are distributing or copying your work without license on a bothersome scale, that's the time to hire a lawyer to:
It's worth noting that some money-making RPG publishers have stopped worrying about "piracy" of their work, as there is a growing body of evidence that its net effect on sales is negligible.
Publishing
As for publishing, the games industry is moving away from up-front print runs and big publishing houses, and moving toward boutique publishing houses (usually at most one or two people), self-publishing, and electronic distribution or print-on-demand (POD) services like Lulu and RPGNow. Even White Wolf, one of the once-great publishers, is now only a few people.
The advantage of print-on-demand is that your up-front financial risk is minimal (and sometimes $0) and you don't have to ship and store a crate of books in your garage; the disadvantage is that the per-unit profit is less due to the larger cut that goes to the printer-publisher (30–40%). Offsetting that per-unit cut, you're usually selling direct to customers so your own percentage is undiminished by wholesale pricing. Print quality used to be a disadvantage too, but for the standard formats the quality of POD books is now very good. And unlike with a novel (and even there not as much as it used to), self-publishing an RPG has no stigma attached to it: the RPG industry has a long history of DIY games being just as good as the "pro" games.
It's also worth knowing that there is no money in RPGs. Unless you become a superstar game designer (there are only two I can think of, and even they have to do non-game work on the side), your games will never be more than a source of pocket change and may in fact be something you pay to keep alive. Wizards of the Coast, the biggest player in the market, barely makes enough money on Dungeons & Dragons to avoid having Hasbro mothball them. Luke Crane, who's one of the few who has achieve publishing stardom independently, is a professional editor and layout designer and has to supplement his earnings from the Burning Wheel with that work.
Keep your day job, do it for love, and ask yourself how much you're willing to lose up-front (scroll down to "Publishing" on that link) before you settle on a publishing route. Some publishing methods are very expensive up-front to the author, and that money isn't guaranteed to be recouped. If your desire is just to have the games published at all and hold the book in your hands, there are many ways to do that now, and some of the cheaper ones may be just as satisfying for you as the more expensive and more traditional 6,000-book print run.
Format
If in doubt, set up your document creation process so that it can generate PDFs if you need it to. There are other formats that traditional publishers accept, but nearly every single one accepts one of the PDF format versions. Besides, if you can generate a PDF of your work, you almost certainly can generate one of the other format they'll accept, whether that's Word, InDesign, or Quark files.