you will need a 20in. long shaft, not a 15in.

the electric start shouldn't matter on the honda because of the charging cable. other brands w/o electric can't charge. That is if you don't mind pull starting.

Make sure with the dealer on the charging cable i am 99.9%sure about that.

On my 2000, 18.5 Lund Tyee; I have a 1998 Mercury kicker, 15 hp, 4 stroke, electric start and tilt with a voltage regulator. With the kicker at WOT, it will push the boat at 9 mph on a clam day. On the size boat that you have, I wouldn’t go any less than a 15 hp, the 15 is only 7.5% of your 250 hp main motor.

I have a 15 h.p Yamaha,4 stroke,electric start,tiller,20 inch shaft,which has been sitting in my cellar for the last 5 years. Motor has less than 25 hours of use it's just like new. I sold my 16 ft.Lund and bought an 18ft. so it's been collecting dust ever since, worth a look. If interested email me.

Just got done dueing this last year. i have an 8 hp merc 4 stroke with elc. start. Push's my 18' cuddy @ 8mph wfo. Plenty for lakes, i also agree with Adrian on the garlock transom mount.buy the black 4 stroke version. Comes with easy formula for mounting instructions,(just sucks drilling holes in the transome, ouch)next you will definately want a controll king our such to controll your speed from the dash...Priceless @ $200.... and an easy install.And an easy steer which conects the two motors together so you steer with the wheel.
Any questions Lemeknow!
Whip