No multi shot option for the AF guns, and none likely any time soon, the inline design of the AF tank/valve makes it damn near impossible. Regarding the rest of your questions, you need to answer one or two first. What is your primary use, and what range will you be using it at?
I've owned single shots and repeaters, I currently have 2 single shots. Much as I liked my Cyclone, I was never in such a target rich environment that a fast follow up shot really mattered. And for targets, you just go through pellets faster :-).
Power, or FPE, depends on what you're shooting. Check out the Hunting Gate, lots of game taken with sub-15 fpe springers. I recently took a fair sized ground hog with a .177 S200 set right at 15 fpe, for me, that was probably a bit of a stretch. I prefer 20 fpe or so for game that size, but that's just me. I happen to like .177's, at around 20 fpe that's plenty of power for anything I'd shoot out to 40 yards. Again, that's just my opinion.
The interchangeable barrels of the AF guns are a nice feature, but don't make your choice based on that feature. There's a lot of fiddling around needed to make one gun work with a 12" .177 barrel and a 24" .22 barrel. You're probably better off with 2 different guns.
Caliber is also dependent on what you're going to be doing with it. Most of my shooting is paper in my back yard, and the occasional hunting I do is served nicely by .177's. But I have self imposed limits on game and range, I'll shoot birds all day at 40 yards, maybe more, ground hog size game stops around 30 yards, and something like a raccoon is 20 yards or less. I wouldn't tackle a pig with an air gun, big bores might be capable, but my .308 damn sure is, those little buggers are MEAN! IF I felt the need to shoot a coyote, I'd put it in the same class as a raccoon. But when's the last time you got within 20 yards of a coyote? Hope that's some help, later.
Dave