RE: Inverted Engine
Higher centers of gravity, certainly do effect roll stability. It won't effect the roll moment of inertia, enough to cause concerns. However, the designer takes these effects into consideration, when he designs the airplane. So, Argess, unless you are designing an airplane for yourself, as a beginner (not recommended) you don't really need to concern yourself about whether the engine is upright, side mounted, or inverted from this standpoint. However, from an ease of operation standpoint, side mount or up right. Leave inverted until you've got some experience.
I am assuming you are a beginner, if not I've meant no disrespect