Like I was saying I wouldn't bring the outboard with me on the 258 it will be used for going short distances around the marina. We have a beach to launch the boat so not an issue there with the heavy motor. There are a bunch of places very close that are quite nice and only very small boats can go there.
I am looking at a mercury 310 which is rate up to 15hp. I know what you are saying about the twitchy factor, I had a 12.5' with a 20hp on it. I loved it but you had to know the limits.
I am thinking there isn't enough room up there for a 9'6". I would do most of the inflating with my electric pump but I like to top off the tubes by hand to get the correct pressure. And like you said there isn't much room up there on the bow.
I did find a mercury 270 which is rated for 4 people(1200lbs) and is only 8'4" and rated for 8hp. That might be a better option. Probably won't plane with the family but as long as I can fight the current and make some headway I will be happy. Currents are in the 5-6mph range right now so it may be slow going upstream.
Unfortunately I think the only way to know for sure if I can do it is actually buy something...

I do love boat shopping even if it is only a tiny inflatable.. still fun.