I have a 20' Lund and use my Merc. 9.9 with my 101# thrust, 36V, Terrova with I-pilot regularly with great success. I can fish by myself, set lines, and net fish without going in circles. I couldn't imagine fishing without it.
You may want to consider a 24 volt. A 12 volt would be ok for a few hours but, fighting wind and Lake O current, it will run your battery down pretty quickly. I have a buddy who has a dump switch that charges his Terrova battery while his big motor is running. That may be a cheaper option to consider.
I would just recommend wearing an inflatable PFD while fishing alone. A boat will get away pretty fast if you slip in and your by yourself. Also, wear your lanyard on you just in-case that does happen, you can spin your rig back around to you.