Your on the right track
I would go with the Minn Kota as well (they weren't out when I bought mine)
I really don't think you need a 160 thou. Or going that big I'd go with 36V
With my front mount trolling motor (80) I can go over 4 mph
And even thou my boat is a 18' Alum
Dry weight is 1485 so motor, gas, 2 guys and gear I'm around 2,500 pounds
I'm told the rule of thumb is 15 pounds of thrust = 1 hp

I've all ready put 50 hours on the main motor
Without the elec. I'd be at 4 to 5 times as many hours

I take allot of fish straight line trolling over 20 FOW
If there's allot of boats out on the weekend I do have to run the inside boards
So the slient part does help.