Definitely get a four stroke motor if you can. I've had different motors and boats and I have a 25 hp mercury attached to a 20 ft Foerster pontoon right now. We have it on a river and it works best for us to have a smaller pontoon and motor because of how shallow the water gets sometimes. We had a 24 ft premier pontoon with a 90 hp Johnson two stroke on it but it sat too low in the water. Kind of a tail dragger with that big motor on it. Lol. That two stroke was always hard to start also. Cold blooded I guess. Anyhow, I really like the four stroke. Wouldn't ever go back to a two. As far as boat size goes it doesn't mater much if you're on a lake and have a good landing available to you. You're going to need a decent trailer also. Get a bunk style if you're going to be driving longer distances to the lake. Or a scissors style is more functional and you don't have to store it on the trailer like you would if it was the bunk style. I think you'll be surprised at how much you like a pontoon boat. I wouldn't go back. Your dad Wil love it too! Steve