It's alright for racing, 3x 16:10 screens would propably be better for a wider FOV and less hassle to setup. That would be too wide for any other kind of gaming if you ask me though, this is a nice compromise for all genres.
Don't know really, you'll just have to research which 17" screens you have in mind to make sure they match your vertical resolution and physical height when rotated to portrait. Dot pitch should also be as close as possible to the main screen.
Depends entirely on your GPU and combined resolution you'll be running.
I'm pretty sure there aren't any precisely 1200 pixel wide screens available for consumers in a standard form. 1152x864 4:3 is as close as I can think of, that would of course result in black bars. The next step would be 1280x960, which doesn't match either.
At work our product is sold pre-loaded onto PC's, which means in the corner we have an equal supply of PCs, monitors, keyboards and mice - easier to grab a whole bundle for testing.
I did try using 1 screen and swapping the inputs (dual input monitor) but it was a pain in the arse.
Keep the second monitor, keep the second pc, get the second mouse and keyboard and hide them. Then you still have an equal amount of everything in the corner.
This is what my boss has, there's a button which you can mount on your desk anywhere, press the button and it will switch to the second PC allowing you to use only one mouse and keyboard between two PC's.
I have the same sort of thing but an older KVM switch, i switch between PC's by press 'Scroll Lock' twice and then the up arrow.
Invest in a switch, trust me, if your planning on keeping the two PC's it makes life A LOT easier.
If you don't change PC often, might I recommend Synergy? I've been using it for a while and it is great, takes a while to get used to as I use it with a laptop and a PC so I keep wanting to use the laptop controls, but once you get into the habit, it is fantastic. It works cross platform too.
Obviously if you change the second machine on a regular basis, installing and setting up Synergy would be a major pain in the balls.
The second machine gets wiped about 5 times a day (right now - a lot less later), can't go on the internet. Doesn't really seem worth going for the solutions above.