Towing
Trailer weight is not as much of a concern as the pin weight. General rule of thumb no matter what kind of trailer, pin/tongue weight should be within your 1/2 half ton (so no more than about 1000 lbs) and should be 10% of the trailer weight. People who pull 5th wheels with half tons tend to scare me (I know the pin weight is more than the truck's legal limit for bed weight). If it's a 5th that is under 10000 lbs weight wise, you should be fine though. I would highly recommend not installing the 5th wheel hitch and instead going with the much stronger gooseneck hide away hitch. By the time its all said and done, the hide-away hitch and the king pin adapter cost about as much as fifth wheel hitch. Plus, if you want to actually use your bed all you have to do is pull a pin in the tire well and pull the 5 lb ball out, flip it over and put it back in. Beats lifting the 5th wheel components.
Yes from the bed. From what I've read on other threads pulling from the bed over the rear wheels is a little easier on the truck by spreading out the hitch weight rather than all the hitch weight just on the very back of the truck
For a little as you would be pulling, a gooseneck hitch with a king pin adapter for the trailer would probably be a good option for you. Little more convenient when it comes to using the bed when your not pulling. From what I've seen lately, the hitch and adapter are the same as your standard 15K lb rated 5th wheel hitch.

