Keep the cef rear seats, they arent too bad. Front ones really anything skyline should fit.
Suspension I personally would recomend getting bilstien stuff, its in my oppinion far superiour to anything else in its price range.
Brakes its all going to fit, just depends on the wheels you get with it. GTR wheels should fit... but seriously they are a lot for whats a 'stock' item. Personally I would get R32 or R33 brakes, whichever you can get cheapest, and spend the money you have saved on brembos on good pads, good brake fuild, a caliper rebuild, braided lines and good slotted disks, this I feel would produce better results. Bang for buck
Engine no idea, I have an R32 RB20 in mine, the oil pressure sender isnt hooked up... Thats about it I think.
Sway bars, get aftermarket only. A gtr one is going to do close enough to squat all. S13 should work.
Digital climate control is apparently SO much of a stuff about as there is an extra sensor on the digi ones, I wouldnt bother its still going to work the same.
Thats about all I can help you with atm.