DaleD, I think the small thrust 12v will work fine for the lakes. I have an older about 10 years now Motorguide 18 lb thrust motor. It would push my alum 11 boat around most of the day when I used it for that. I may some day put it on my southfork pontoon, Havent decided yet on that.
So i think if you went with a 25 or lower thrust motor you should be fine. A group 24 deep cycle is what you will need. Get a box for it and screw the box to a board or alum deck so it wont slide around. Good luck, if I see someone a shooting rooster tail off the back of their pontoon I will know it's you.