Roydawn, you should be fine with the regular 9.9 or 8. If there is any question, just get a low pitched prop for the periods you need to push the 25. I have told the story many times I got our 65,000 lb ketch moving 2.5 knots with a 4.5 hp motor on the hard dinghy, and then when I got the 13 foot inflatable blown up and the 25 hp on it, we got up to over 5 knots.
The high thrust is not of much value on the dinghy, at least for planing.
Where I think one may have a problem with the Honda, is gong to be where the tanks are under the floorboards. Such as in the Tom Cat, or the C Dory 25. You may be fine. Worth giving a try.
No issue with the Air conditioner and the dinghy. We rarely ran the roof top when we were under way. At anchor, or marina, usually the dinghy was either in the water, or we raised it up, so that there was plenty of ventilation for the Air conditioner. I just think that the RV Air conditioner is so much simpler, no water pump, no worry about plugging up the intake (and that is a real issue, with jelly fish, sea weed, kelp, small fish, mud etc.) Rv is much cheaper, and you don't give up a storage area.
But just my opinion.