Regarding your question about moving engines around. I have an engine for each plane that I have. Now I only have 6 and am building my 7th, so I might change my opinion as I get more. However, I like to have all my planes, including trainers, ready to fly anytime that I get the urge to do so. There are days where I just want to take out my easy flyers and kick around. Then there are those that I really want to practice aerobatics/3D etc. I would not want to be moving engines around constantly. I will add, though, that several of my engines have been on more than one plane, I just don't have that particular plane anymore. (you can guess why not)