Here is a source for info on folding and inflatable canoes and kayaks in case you haven't seen it already.
http://www.paddling.net/We have an Innova inflatable kayak and it is a pretty reasonable little boat. We generally just dry it off with a towel - that seems to be adequate.
Manual air pumps are slowwwww. We use an electric and then get final pressure with the manual foot pump. Some models require pretty high pressures (more than 5 lbs pressure). This gives you a more rigid craft, but must be harder to pump up.
Flat-bottomed boats are almost impossible to steer in a wind. If the boat doesn't have rounded or shallow V-shaped hull, then a rudder or skeg is necessary.
Kayaks can pick up a lot of water from the paddles. It is nice to have raised seats or to add seats to keep from having to sit in a puddle.
A fully inflated boat can over-pressurize and even pop in a hot sun. It's a good idea to depressurize when you are not using it.