Sounds like you have almost the same boat setup as me. Mine’s an 83 Lund s-14 dlx with Johnson 25 HP that pushes it 24.5 by myself and 22-24 with another person, depending on their weight. I also finished mine off building a front casting deck and a bow mount platform with composite plywood and outdoor carpet. Cranking battery in the back and trolling motor/HDS battery in the bow battery compartment I built.
Get to the point already… 12v 55 lb thrust is PLENTY for this boat. I run a 12v 35 lb thrust bow mount and get .7-.9 mph on 20% power and 3.5 mph at 100% on flat water. With a 35 lb thrust transom mount, the slowest speed put me over 1 mph on flat water. These boats are really light and it doesn’t take much trolling motor power to pull them around.
I power mine with the cheapest fleet farm brand deep cycle battery, assuming group 24, and have NEVER come close to running it dead in a day of fishing… Even with powering my HDS off the same battery. I fish muskies a lot and that means I’m on the trolling motor all day. Never run out of juice.