The .25 FX is a hot little engine, and would probably fly a .40 size trainer nicely in the hands of a pilot with a little bit of experience. For all I know, it may fly it well for a beginner too. But yes, the recommendation is to go a bit bigger.

There are lots of threads on RCU about the merits of 2 and 4 stroke engines. For your purposes, pretty much the perfect engine is an OS .46 AX. It has more power than you need, will transition to a sportier plan when you are ready, and is very reliable and easy to tune. Alternately, you could go electric with a .40 equivalent brushless motor and appropriate batteries and a charger. That route costs more money, but it's more convenient.