On the one occasion we started a new group from scratch, we all went out to dinner together, during which we talked about what we were looking for in a game and did some basic worldbuilding. Also, it meant hanging out in a social situation and just getting to know each other. If it didn't end up working out, I believe it would be a softer rejection this way, either with me deciding it was the wrong group for me or with the rest of us potentially deciding to leave someone out.
It was clear that this was sort of a casual gamer interview for each other, but not in the high stakes way that a job interview would be. In our planning email, I was upfront about just making sure that we had some basic social compatibility.
My group uses a private Google+ community to organise the games, and G+ alongside Roll20 to play the games. We play entirely online on a weekly basis, mainly because we're all about the same age and have small children and families, so it's difficult to get together for a face to face game.
For D&D 5th Ed you're pretty spoiled for choice, but when it all boils down the best two options are this:
Roll20, either in conjunction with G+ or on it's own. You can create an account and run your campaign through it for free, and the biggest pro (in my opinion) was the ease of use when it integrates with G+. Most everyone has a google account these days, so they also have a G+ account whether they know it or not. Once you've created your game in Roll20, you can choose to launch it in a g+ hangout.
Once you've done that for the first time, whenever you launch a G+ hangout the Roll20 app will be present, and you can launch it and select your campaign from within the hangout. Running the game each week becomes as simple as scheduling a G+ hangout event and showing up - the players don't even need Roll20 accounts, they just click the hangout invite link and game on. The D&D 5e character sheet for Roll20 seems pretty excellent too, with some dice rolling automation built into it. We're taking it for a test run soon hopefully.
The other main option right now, though it can get pricy, is Fantasy Grounds. It's not as simple for the players as Roll20 (which is, as i've said, just a link click), but if they're willing to install the program (available on Steam now as well), Fantasy Grounds is now the official online tool for D&D 5th, in partnership with Wizards of the Coast. It has excellent integration with the rules system and character sheets, as well as supporting hero lab. Some friends of mine swear by it, though it is a bit more complicated to get set up and running.
Both solutions support full voice, and I know Roll20 supports full video both in the app itself and through hangouts, as well as an online tabletop for maps, images, handouts and whatever else you like. This made it a lot easier for us to retain that "social tabletop" feeling, despite playing entirely remote. Using a large enough screen and a good set of speakers and microphone, you could play partial remote (with only a few players remote) or even with everyone in the room and disabling the voice and video altogether if you wanted.
Either way, if you do plan on getting in to running your games online through virtual tabletops, Google+ is your friend! There is a massive community of people there who will be more than happy to lend any assistance required.
Personally, I run a community geared at assisting people to set up, run or find games in the asia-pacific time zones. You can find it here: https://plus.google.com/u/0/communities/100566740249118526694
For other timezones, such as the American zones, a great place to start is here: https://plus.google.com/u/0/communities/107422815813208456454 It's an excellent community filled with friendly people.
Best Answer
The Restriction you're suggesting is a strict subset of the allowed rules in Adventurer's League Play
5th Edition Adventurer's League has a "PHB +1" rule for character creation, that requires that each character created for AL play be based only on materials found in
So your rule is a strict subset of that rule: of the officially published 5th Edition sourcebooks, you are only permitting Sword Coast Adventurer's Guide, for all characters. As such, while it's more restrictive than normal AL rules, it's definitely not absurd or unreasonable.
SCAG is probably a good pick for the restriction
Sword Coast Adventurer's Guide is unique compared to other Sourcebooks in that of the sourcebooks in the game, it focuses more on augmenting existing PHB material rather than providing whole new options wholecloth.
For example, unlike the other 5e sourcebooks, SCAG's only Racial options are variants on existing PHB races: Dwarves, Gnomes, Half-Elves, Halflings, and Tieflings
The only new spells SCAG offers are some (admittedly very powerful) melee-focused cantrips for Wizards, Warlocks, and Sorcerers
SCAG only introduces a small number of additional class archetypes, one each, for Barbarian, Cleric, Fighter, Monk, Paladin, Warlock, and Wizard. It also has two for Rogue and one for Sorcerer and one for Monk that were later reprinted in Xanathar's Guide to Everything.
And SCAG offers a fair number of new Background options, which were already customizable as-written in the PHB.
So if the goal is to keep character creation from getting overly complicated, limiting to the PHB and SCAG is a valid option.
Personal Experience: Allowing 5e sourcebooks, disallowing Unearthed Arcana or Homebrew, is pretty manageable for new players
The big "Expansion Sourcebook" in 5e is Xanathar's Guide to Everything, which contains multiple class archetypes for all of the 5th edition classes, has lots of new spells, has lots of new racial options, and also contains a lot of variant rules for DMs to use. So if you're worried about complexity, that's definitely the big one to watch out for; most of the other sourcebooks contain about as much player material as SCAG.
Having said that though, the options provided in Xanathar's (and the other 5th edition books) has been, in my experience, pretty manageable by players. The trick is assuring players that try to use any of these books that most of the material found in these books, even in Xanathar's, is flavor text that they don't need when creating their character (or at least they can ignore while they're trying to work out, mechanically, what they want to play). If you go through and enumerate/index each of the choices that are actually offered by each book, it'll make these choices easier for players.
That last point is important: it's a lot easier to figure out "what kind of Paladin do I want to be?" if you can choose from a specific list, i.e.
As opposed to trying to search through each book for the specific sections that describe each of those archetypes. If you put together lists like this for each class/racial option, your players will be a lot less overwhelmed by the choices they're being offered.
The one risk is background or class options that clash with your campaign: Guildmasters' Guide to Ravnica, for example, offers some Background options that are extremely enticing (especially for spellcasters), but which probably won't mesh well with any non-Ravnica based campaign. Other books have similar restrictions; SCAG, for example, offers the Bladesinger class to Wizards, which normally is restricted to elves and half-elves only. There's nothing stopping you, as DM, from lifting that restriction (and indeed, the text as seen in SCAG literally suggests lifting that restriction to suit the campaign if needed) but this is one more example of how you might need to tweak things or set ad-hoc rules on what players are or are not allowed to take.
So it's up to you. PHB + SCAG is definitely a reasonable restriction, but most newer players won't be too overwhelmed by allowing the other 5th edition sourcebooks as well, just plan to index the contents of Xanathar's Guide to Everything if you do decide to allow it, to make picking options out of it a little easier.