How can I check I all my flights plans so that they will work and won't have problems like , no parking space, airport doesn't exist yet, can't fly or will crash on air as it use same flight plan as another flight, what tool can do this for me?
When you're recompiling your traffic.bgl file, TTools will stop and giving you an error if it can't find the airport, or the plane. AI planes never crash in the air (they usually just go through each other), but the PAI flightplans are created just so that you shouldn't have this error in the first place.
Can I have both default ms flight plans and project AI?
Yep.
What is a painkit, RAFCAD and AFCAD?
A paintkit is a blank plane which you use to paint over in the colours of whichever airline you want.
I'm not entirely sure about RAFCAD, I think it's something to try and get all the airlines to park in exactly the right places as in real life, but I'm not sure.
AFCAD is an airport designer program - it creates parking spaces at an airport, lets the AI planes know which taxiway to use, etc, etc.
Can I install multiple PAI files with installer v2?
Not at the same time, I think, but yes, you can install lots of PAI files seperately.
Does anyone know if there is any fingers in airports?
Do you mean the walkways from the airports to the planes? If so, then no, there aren't any in the PAI files. Some of the default airports have them, and some add-on airports have them, too. But most default ones don't.
And ground crew?
Sorry, no. None of the default airports have a ground crew, but there's a number of add-on airports and add-on programs (like LAGO's Flight Simulator Scenery Enhancer) which will give you a static ground crew. The only disadvantage is that they don't move!