While they call them "trolling motors" and they can be used as such, in my experience they aren't really the best tool for the job. Depending on tide and breeze you will have a 100ah battery pretty much flat in a couple of hours on that size boat. I would be looking at other options - a "kicker" or auxiliary engine, a trolling plate or simply even dragging a bucket. Running your engine in a tilted position will wash off speed as well. If you do a heap of casting as well, then an electric with spot lock is worth it's weight in gold.
If you are really into trolling and are looking to spend some money on a tool to make life easier, give some serious consideration to an autopilot. I ran one on a 4.5 centre console for years, initially with mechanical steering and then changed over to hydraulic when I got sick of cables rusting up. Makes a day out dragging lures or live baits a much more relaxed exercise.