I used to launch my jet-ski at Lee's Ferry and use it to run up-river way back in the day...
You should have seen some of the incredulous looks I would get from the snobby Orvis Fly-fishing crowd. I loved every minute of it.
Bill- my best pieces of advice-
1) Like you said- get a 3-seater for stability, fuel capacity and range.
2) Get a four stroke for reliability, MPG, and ease of maintenance. 2-strokes are for going fast.
3) Yamaha's and Hondas have the best keel design for stability in rougher water, IMHO. Sea Doos and Kawasaki's are performance inspired hulls better oriented for speed and maneuverability.
Finding one will be easy - Craigslist is LOADED with jetskis for sale
All of the current manufacturer's 3 seaters have excellent stability....but would have to disagree on your order of preference for rough water......( I've ridden Seadoo in Penasco, out to Bird Island, and even out to Catalina Island from Long Beach)
1. SeaDoo/Kawasaki
2.
3. Yamaha
4. Honda (does Honda even make a true 3 seater???)
:stir:
They are all self righting if you roll, ..... The closest I've ever come to rolling mine was riding 3 up, making a very sharp turn at slow speed, without giving enough throttle....we all slid off, and the jetski righted itself.
If you get the 4 strokes WITHOUT supercharger/turbos, they have decent fuel economy...but don't expect much over 7-8 mpg. Most have 14-16 gal. fuel tanks....a couple of the new models have even gone to bigger tanks. There were a couple models made that were even bigger then a standard 3 seater....I think Yamaha called theirs an SUV or something like that...with a bigger tank. I rode my 4 stroke supercharged Seadoo out to Bird Island, tooled around a little bit out there, and still had fuel left when I got back. My daughter's 2 stroke, fuel injected/direct oil injection, has even better fuel economy then my 4 stroke. The trip out was pretty calm, doing about 35-40 mph, the return was slogging into heavy seas... about 15-20 mph.
I've seen a few interesting rigs for fishing....just Google "jetski fishing rigs".....