What tasks are to be run on this 'control computer' behind the pit?
Options for running all those screens is probably best to be left down to these options:
2 graphics cards (ones that will work in SLI) and run 2 screens off one of them and the control screen off the other. If you use two different cards such as a powerful one and a weak one, I think it might cost your system in performance... Or it might not allow you to use both. I'm not too sure.
A Matrox TripleHead2Go type set up. A powerful card then run 3 screens off of that. Never messed with Matrox stuff before so I can't say how easy it would be to get it to work.
The sticky for building guide has some links to software that will run gauges. I think CockpitWare is one of them. There are definately some which let you run a seperate program to just run gauges. Then re-position them how you like and stick some casing over the top to make it look more analogue-like.
Hardware is probably just anything as cheap as you can get. No point forking out loads for throttles and sticks etc. Check a bargain shop or maybe even your local recycling centre to see if they have anything available. I was able to get a free computer from our recycling centre, though it took some persuading as they do get points for recycling more. I told them it was for my GCSE Product Design product (and it was at the time. Then my design went downhill) so if you tell them it is for an ATC project they should allow it. Well, let's hope so.
The rest, I suppose, is resting on what you want it to do. What features should it have? What tasks will all the sections do? Does it need buttons for radios, landing gears, etc?
I hope this is a bit of help. Our ATC cockpit plan isn't really going anywhere for a while though
. Rest is just up to you to say what things you want it to do, then I am sure one of the experts here can give you the best option for it.
Best of luck.