Avistars are outstanding trainers. They are the number one recommended plane for beginners at my club. You can fly it with any .40-.46 engine, but I'll suggest getting a ball bearing type .46 for it like the OS .46 AX. You'll have a shorter takeoff roll and more power to recover from stalls with which is nice, but the biggest benefit is that you'll eventually graduate to a sport plane which will need the extra power. Being able to use your existing engine is a big plus during that start up time when money is frequently tight.