Why buy a second rate engine, if you can afford it, get the OS .46fx for your 40 size trainer. When you get to the field, you won't have to fiddle with the engine, you can just go and learn to fly. The stick on the left is the throttle, so you don't need a low power engine for your trainer. That way you will also already have the powerfull engine you will want for your second plane. There are a lot of other engines that you may or may not get a "good one", you will not hear people bad mouth an OS if they have one(other than the bad batch of liners they had some time ago). I agree with the part about getting in your local flying club, you'll get a lot of good advice there. Watch what other people are using, and how much trouble they have, then make your own decisions.