First of all thats the plane im talking about, its not the nicest looking plane but it flies so smooth for a beginner and builds really nice (Most pieces are already shaped ie leading edge elevator airleons etc..)
I really suggest getting a kit over an ARF for a trainer for many reasons.
1) Cheaper
2) You learn so much from building a kit and it will definetly help you if u plan to build the Piper as a second plane. (Or if you want to go with a Top flite Cessna.
3) It gives you a reason to be proud of your plane. (with an ARF you can say i can fly an RC, with a kit you can say i can build/fly an RC). It also gives you an understanding of the aerodynamics of the plane.

Im not sure but by gas do you mean glow?

If so i would suggest getting a glow trainer like ones i suggested. My opinion id probably alot of people would agree with me (some might not) but glow planes are just overall better planes theyre bigger faster and run for longer periods of time.

If your a little short on cash and not sure if this is the hobby for you go with the OS .40 LA engine and 4 channel radio.
I wouldnt suggest getting i cheap engine because they can just get plain annoying OS is a good manufactuer. If you got a little more spending money and know this is our hobby i would go with a .40 FX the LA will fly the trainer very nice but theres no added power and a FX will be nice to transfer to your sport plane of whatever. A .46 LA will be ok to and a little cheaper the FX.
For the radio Futaba is usually the best for beginners for the simple fact that everyone has it and hooking up a buddy box to it wouldnt be a problem.


Hope this helps,

Papa

P.S. Most of these points are my suggestions and opinions some people will agree some people wont. I personally have all these items and ive been very happy with all of them.