katief7,
I have no personal experience with a trolling motor on a pontoon boat, so I can't offer an opinion on how much is enough thrust. But in principle its better to have too much available and not use it than to have too little available when you want it. .... I looked at the owner's manual for the motor you mentioned and three things come to mind. First, its cool that it has an autopilot function for steering. That solves one of the problems you'd otherwise face in steering with a trolling motor. Second, it is a 36 volt motor so it will require you to install, use and recharge three 12 volt batteries. That will add significant weight and cost to your plan. Third, you will need to use very heavy gauge wire and place the batteries relatively close to the motor to deal with the large amperage and voltage the motor requires. Keep that in mind as you decide where to mount the motor and batteries for the best balance and operation of your boat.
Good luck on the new lake.