Take a walk through with the home inspector and see what he says. If you are still interested in the house, find a good general contractor (that you trust) and take him on a walk through. The contractor should be able to give you a good estimate on what it will cost to fix any issues, he may also give you some price breaks if you are willing to let him handle all the work.
Just make sure you are comfortable with the contractor before you ask them to go on the walk through, they might be upset if they take time to walk through with you and then you find a new contractor to do the work. Keep in mind, however, that if the contractor starts work and does a sub-par job, you can always fire him and find a new contractor.
It's not real critical. When wiring phone centers we used metal raceways (or a thrown-together wood one) in the ceiling, but for my house I used pipe clamps like the one you posted at about 4' spacing. I like to add a wrap of double-sided velcro around bundles going to the same box, also about every 4'. Near the demarcation point I might use a few screw-in hooks like those used to hang bicycles if there are a lot of cables going out in one direction.
Don't fasten the cables to anything too securely. That way you can use the old cables to pull a new one if it becomes necessary.
One important detail: do not use zip ties. They can constrict over time and damage the cables they're wrapped around. (They're also tougher to pull new cables through than velcro loops.)
You didn't ask about routing them, but I guess it's relevant to explain the assumptions my recommendations are based on. I always do horizontal runs in the floor/ceiling and then run vertically within the bay where the junction box is located. (Rather than meandering through the wall as shown in one of pumpkin's photos.) This means less holes to drill and usually less resistance when pulling the cables. I also leave an empty bay (two studs) between mains and network cables, so I don't need to worry about securing the drops (recommended distance is at least 1' apart when running parallel to mains).
If you wanted to make pulling new cables even easier without doing a full PVC conduit setup, you can just install PVC fittings such as 90° elbows where the cables pass through the top plate or sole plate. That's were all the friction is going to come from when pulling, so some nice smooth PVC lining the holes can smooth things out nicely. (This of course assumes you'll use one of the existing cables to pull the new ones. Obviously you won't be able to run a fish tape without the sections of PVC connecting the fittings.) The fittings would also ensure that you don't go under the cable's minimum bend radius of 1 inch.
One other thing that I'll mention just in case is heat. Large, tightly-wrapped bundles of cable (think 50+ cables) that are being heavily utilized have the potential to trap heat in the center which can eventually degrade the insulation and cause shorts. Unless you're running a grid computing cluster at your house that's not likely to be a problem though. A more likely scenario for the average home owner is the use of Power over Ethernet, which will generate more heat. If you're planning to use PoE I'd limit bundles to 7 or 8 cables, just for good measure, even though I think the odds of a problem are still very low.
Best Answer
Most of your questions are the same question, just asked in a different form.
Before you even start looking -- Before you even find a realtor -- Do your research on a good home inspector in your area. If you are looking at an old house, make SURE to tell the home inspection service that you want someone who knows about houses xxxx years old. Most inspectors of newer (1-40 years) houses think everything in an old house needs replacement and will give a bad review of everything. Then get references and talk to people he's worked for. If he's not willing to give you references, then move on. When you find an inspector, go with them to the house & follow them around. You will learn a lot more than what will be written on the report, whether you buy the house or not.
Generally, you've got to look at the following areas:
Essentially, you don't want to mess with 1 and 3 at all, and the remainder, you need a good estimate of the costs.
The next important detail is Architecture. Are the rooms of appropriate size or is the floor plan easily convertible to something you can live with and enjoy.
I haven't included cosmetics at all. Because this is where you are going to do it yourself.
Money you can't avoid: