Just an opinion
Ahoy John,I had a Cat 22 -- had a Suzuki 6hp, two stroke.  Worked fine.  Actually, the Suzuki was about the best starting and running OB that I've ever had, but this isn't a commercial.I do see still some folks with 8 and 9 HP engines on 22s.  Overkill in my opinion.  And it sounds like you might be thinking four stroke?  An 8 or 9 HP four stroke is really too big in my opinion, but I see people doing it.  Just have someone ride on the bow I guess to counter act the weight of the motor.The alternator?  Really depends how much you run the engine.  If you are just putt-putting in and out of the marina, the alternator may not do you as much good, as say, a 10 watt solar panel.Good luck,Brad