Most any trainer plane will do the job, but we all have our favorites. I have a lot of stick time on SIG LT-40's. That's been the plane of choice for the youth group I instruct for. I learned to fly on a PT-40, so I'm also partial to that one. If you have a local hobby shop, ask them. They know what they either have or can get quickly, plus they'll usually know what equipment is preferred by the local club instructors. If possible, talk with whoever will be teaching you. That's the best way I know to select equipment.
AS for equiping the biplanes, have you considered doing the pup as an electric? It sounds like a good candidate for it. I don't do electrics, so I know very little about the equipment.
The engine choice for the Pitts sounds about right. You will probably want a 11x6 or a 10x7 prop. Your engine manual should have prop requirements in it. Measure across the opening that the engine shaft will be coming out of the cowl through. That's the size spinner you'll need. Standard size servos should work fine for the Pitts, but you may want to go with smaller (lighter) ones in the pup. Once again, talking to local club members is your best bet. They'll be glad to look and to offer advice.