OK
1st)  Your limited to what size TV you can put in your cab by the width of your cab.  I was able to put a 27" Zenith TV in my cab, but I have a shave the insides of the cab to get the TV to fit.  
So I suggest you get a TV that doesn't have a speakers on the side but on the bottom.  Therefore you can get the maximum TV width.  Also try to get one that has Video 1 & Video 2 inputs.
2nd)  I use my Cab to run PC, Mame, PS2, Xbox, Sege Genesis & Dreamcast systems.  I have my the S/Video out from my video card plugged into my "Video 1" input on my TV.  Then I purchased a S/Video "System Selector" from Walmart for @ $20.  And plugged in all the A/V cables from the consoles to the "System Selector" and the System Selector output is plugged into the "Video 2" input on my TV.
So if I want to watch TV, then I put the TV on normal.  If I want to use my PC to play Mame, then I select "Video 1" on the TV.  If I want to play any console games, then I select "Video 2" on the TV and I select whatever console I want to play via the "System Selector"
Also,I bought 2 Act-Labs TV light guns and they work great.  
Hope this helps.
-GGKoul