There are several issues regarding an inflatable and a motor (trailering, outboard portability, rowing frame, boat balance, pontoon/bottom durability, cavitation of the jet etc.). The guys at Alaska Raft and Kayak have the most experience and willingness to help from what I've gathered in my research. They can help you. I am/have been looking for something similar because I want something to run rivers but not have to trailer a craft. I also wanted something large enough for two guys with gear or four adults for a day trip. Boat size and horsepower become an issue (especially with a jet) when trying to balance portability of the craft (like when I assemble and launch by myself).
The Zodiac Grand Raid is the model to pursue in the Zodiac line from what I understand. There is also a boat called an Alaskan Jet Ranger that might give you something additional to consider. Another possibility is a Dux Boat.
You can find additional information on the outdoorsdirectory.com under the boating and hunting forums. Lots of guys on this site have first hand experience and can give you tons of helpful information to help you consider everything before you drop any cash.
Mercury makes a 25/20 hp jet.
Hope this helps some. I'm still banging my head against the wall...
P.S. Unfortunately, I have never talked with a motorized sport boat (who is a river runner) that would do it again vs. going with an aluminum boat and a jet.