My 16 Tracker was rated for a 90, but came with a 40, which overall I was happy with and it was a gas sipper. I did put a Piranha power prop on it as it would not plane with three guys and gear in it before.
The kicker may come in handy if you need to do a little faster trolling. I used to have my 6 hp kicker just above an idle (to where I could still pull start it without changing the throttle or gear shift) with the steering locked down and used the bow mount Terrova for directional control. It worked great that way.
The current 19' boat I have has probably twice the HP (175) it needs, but I do not use it all unless I want to get somewhere quickly as it sucks a lot of fuel.
I use the kicker and bow mount combo often with it.
Try your boat first and see how you like it as is. It may be fine as is.