I have a 17 ft starcraft with a 90hp and was using a 1976 6 hp Johnson as a kicker and it worked great for years trolling with just the riggers or planer boards but once I started using wire Dipsey rods I could not maintain enough speed while going against the down currents to get a 2.5 down speed on the depth raider. I upgraded to a 9.9 4 stroke kicker and that works great and burns less the 1/2 the gas trolling then what the Johnson did, The only negative to going with the bigger kicker was the added weight on the back but my boat does handle it so I've been happy with it.
I have a 17 ft starcraft with a kicker and just us the 90hp main motor to steer while trolling as it acts as a rudder and works good. The only time I may have to reach back and move the kicker a little is when trying to troll against a strong wind\med waves which I try not to do anyhow with a smaller boat.