For rivers, I have a 9', 1 man cataraft, and a 2.5 horse little kicker for getting across lakes and such. It's mostly for fishing and fun. We had a 17', but sold it a couple years ago.... need another one soon.
For a serious boat to get out on the ocean, trolling, river running, etc. I would go with an inflatable, very much more forgiving when it comes to rocks. And it depends on the rivers you want to run, some are more forgiving than others. I would recommend something 16' plus for running on the ocean. Anything 25-60HP is great for that size of boat, just depends on how fast you want to go, and with gas prices, get a kicker for trolling, it's worth it.
The main point of a jet is to get into shallow water, because the water is sucked from the bottom of the jet, and shot through with a contained propeller. I've seen light boats with jets up on step running in 2-3" of water. I know a few people who get a riser mount, to mount their normal outboard higher, and then put a jet foot on it. A jet foot just contains the propeller, and turns it into a jet pretty much, and all for the point of running more shallow.