Billy the kid

Hey guys, I'm looking for some help with selecting the right kicker motor. It will be going on a 17' Doral, closed bow with a 120hp Merc I/O. Though I hope to move up to a 20'-24' boat in the next few years. Last year was my first season trolling for salmon on Lady-O and I was happy with my I/O. She ran 2.2-3.0mph no problem and Fuel economy was decent, 13-36L per trip with an average of 28L burnt in a 8 hour trip. Mind ya I fished in 150FOW or less most of the time. At first I wanted to stay away from a kicker motor as space and overall stability is limited but with the prospect of spring fishing, some world class Walleye fishing in our backyard, and the assurance of a backup motor I'm now looking for a kicker/ auxiliary Primarily looking at a 9.9hp long shaft, but with the 6hp models weighing about half, I haven't ruled them out. Was thinking if i go with the 9.9 I could move my batteries to the bow on the opposite side to balance the weight out a bit. The three brands I'm considering are Suzuki, Yamaha, and Honda. I like the price on the suzuki, the shifter on the Yamaha, and the 12a alternator on the Honda 9.9hp. Suzuki also offers a 12a alternator on their 15hp which is about the same size and weight of the others 9.9hp. A Suzuki 15hp EFI,electric start, long shaft, standard thrust, with a 12a alternator is about $1000 (CAD) cheaper than the Honda 9.9hp carburated, electric start, long shaft, 12a alternator, which is a high thrust. Are the Honda's that much smoother and quieter? Will the high thrust model preform much better in this application? Would a 6hp model best for this boat? If I was to forget about a larger boat in the future for now. Could I get away with a 6a alternator running a 9" sonar and a VHF radio on a 8-12hour trip? I mean I guess that's what everyone did in years past.The only reason I'm looking at an electric start model is for the higher amp alternator as this option seems to add 15lbs to the units. Any input or past experience is greatly appreciated Hope to be chatting baits and posting reports with you guys in the next few weeks, fingers crossed. Thanks