What's your definition of "slow troll". Barely moving in search of crappies is one definition. Slow trolling for walleye is quite another and may range from barely moving to 2.5 - 3 mph. For really slow trolling you need a bow mounted electric troller. Anything from 2 mph on up you can use the main engine provided it is not a 150 HP beast. 40's, 50's and even 75's will troll down nicely on a pontoon.
I have a 19 footer that I have a bow mounted MinnKota 55 Autopilot on that will troll from dawn to dusk on 1 charge of a good group 27 trolling specific battery.
I pull live bait at what we call "dead slow" which is just fast enough to maintain control of the boat.
You will not drag a pontoon around all day at 3 MPH with an electric troller unless you have a minimum of two large deep cycles. A pontoon is like a barn door when it gets into the wind so that eats electrical power.
Trolling plates are not used with electric motors because they are not needed. They are simply a plate that drops down in back of an outboard or stern drive propeller to decrease its efficiency to slow the boat. They are typically used on boats with larger engines that simply can't be slowed enough with the throttle . Sort of like dragging a bucket behind the boat.