Well, since Backwater Charlie already spoiled it for you, I'll answer your bonus questions first.
1 ) No. It's not possible at all. Float tubes are not in the water long enough, not even after a whole eight, ten, or twelve-hour day of fishing.
2 ) Yes. Small fish will even spin you around.
3 ) Forty-four-pound, eight-ounce carp. Fifty-two inches long.
4 ) Not at all, I like a challenge.
I was fishing for bass from my old Fish Cat 4 float tube using a six-inch, Texas-rigged oxblood/red flake plastic worm and eight-pound line. I'm cruising the shoreline in my tube, casting my worm out to the side into deeper water and slowly bouncing it back at an angle. I don't feel any tapping, I don't feel a hit, I don't feel the bite at all. It was just a nice, hard jerk followed by a hell of a run. When I reared back and set the hook, I thought I had hooked THE bass, but after a couple seconds of that long run, I figured out what it was. 2 1/2 hours later after being dragged around this arm of the lake, I finally tire out the fish and get it onto my tube. Both it's head and tail hung six inches off each side of my tube. 44-8 is what it weighed after I got it to a scale at the marina. I was using a 5 1/2 foot Fenwick Fenglass Lunkerstick 2000 rod and an Ambassadeur 2500C reel. It was an AWESOME experience!
*sparks up a cig and commences to answering the important questions*
1 ) Wood River. Before they went out of business, their cheapest model, the v-shaped U-Boat started off at $350.00 and went all the way up to almost seven hundred. Now, it would have to be OutCast. Their top of the line tube is the Prowler, $499. I use an older Fish Cat 4 and it's an absolutely GREAT tube.
2 ) To me, any other company besides OutCast. That's an opinion.
3 ) Wood River, OutCast, Caddis, Water Skeeter, Creek Company, etc; in that order.
4 ) $149 to $250. When my tube first came out, it sold for $149. Now the new model, Fish Cat 4-LCS, is $189.
5 ) A whole assortment of accessories. Specialty rod holders (fly, spinning, and baitcasting), rod tethers, anchors and anchoring systems, depth/fish finders, GPS systems, trolling motors, stripping aprons, storage bags, etc. I personally arm mine with two rod holders and a Fishin' Buddy depth finder. Straps hold all three onto the tube.
6 ) Not usually. Some stores offer deals where tubes come with both fins and a pump, or one or the other. A good set of "premium float tube fins" will cost you in excess of a hundred bucks. Regular diving fins work just as well, only the true float tube fins give off more thrust on the up and down stroke. Double-action air pumps (blow air into the tube on both up and down strokes) are cheap, $25.
7 ) No. Those are always sold separate.
8 ) Yes. With the right type of valve and pump, you can inflate a float tube in less than two minutes.
9 ) Yes. Thirty seconds at most, then you have to push down or roll them up to completely get the air out. Easier to store that way.
10 ) Yes. In a pick up, as long as its tied down WELL (float tubes aren't very aerodynamic) and the vehicle isn't being driven too fast, it's safe.
11 ) No. The materials good tubes are made from does not tear easy. A lot of them have vinyl on the underside for extra protection from bottom, rocks, sticks, fish spines, etc.
12 ) Very. I don't know how to swim at all and I trust one of these with my life, as long as I have my life vest handy. I keep in the "front deck" instead of actually wearing it. I trust it it more than I trust a canoe or a kayak.
13 ) The better brands are. Josh said they aren't fast... V-shaped tubes aren't fast per se compared to a boat, but when you have your legs in the water and you're kicking around, you'll be surprised how "fast" you can actually go. Put it this way, you'll leave a small wake and water will slap the hull. Round tubes ARE in fact slow. Ugh... stay away from those pigs.
14 ) Yes. A lot of float tubes have inflatable seats that make you sit higher, see farther, and stay drier, which is a plus when you're wearing waders.
15 ) Very fun. Fishing especially. Imagine being pulled around for two and a half hours by a fish longer than the tube is wide and more than three times its own inflated weight. Gives a whole new meaning to the phrase, "Nantucket Sleigh Ride". They're not just only fun to fish out of, but they're great for just kicking around in and exploring shallow areas or spots closed to boats. Its great exercize too.
So you have five hundred bucks to spend. Okay.
Tube:
Outcast Fish Cat 4-LCS - $189
Accessories:
Double-action hand pump - $25
Float tube anchor package - $32
Float tube cooler bag/dry storage - $69
Float tube bag - $69
Scotty rod holders** - $16 to $55
Angler's Inflatable PFD* - $120
Rearming kit for PFD* - $25
Outcast Fins - $35
Package Total: $476
*not included in price
**$28.50 for Baitcasting rod holder x 2
http://www.outcastboats.com/outcast/