Alvin,

I agree with the previous posters.

Here you can find more answers to your questions:

http://www.futaba-rc.com/faq/index.html

Used 72 MHz radio equipment can be found in our RCU Buy and Sell.
A FM 8 channel including crystal can be found for $30 there.
High or low band need to be considered, if you are switching crystals in most receivers (switching crystals in a transmitter is a no-no).

http://www.rcuniverse.com/market/category.cfm?catID=122

FM is good enough and PCM has higher resistance against interference.

With so many fliers using 2.7 GHz, interference for 72's users is almost null.

Now, for the Aerodynamics of your question:
Trainers have wings with enough lift capacity as for not needing flaps for landings and take-off's.

This article about RC flying with flaps is interesting:

http://www.modelairplanenews.com/Med...ager/flaps.pdf