If you have room for the batteries Mike 24 volt is way better than the 12. I have run a 24 v 70lb off of the starting and second battery in series for 3 yrs now without any issues. I know a lot of guys say they get interference on their finders doing that but I have never had any problems at all.
I have always preferred Minn Kota motors but don't know much about the new ones except they cost a bunch $$.
Some of the other guys probably have some good advice.
I agree that more is a lot better than too little.