Welcome to sailnet...
A lot of it depends on where you take the courses... since some schools aren't as good as others.
One problem with not having a boat and not sailing on a fairly regular basis is the skills and knowledge tend to fade a bit. I wouldn't recommend bareboat chartering a catamaran until you've gotten a bit more experience sailing than a summer's worth of courses will give you. Spreading the courses out, as suggested by NOLATOM, would probably be a good idea. Another suggestion would be to take the courses in different sailing locations... since the conditions will be fairly varied by doing that.
It would help if you said where you are located, since if you live in a coastal area or with large lakes, you might want to buy a small cruising sailboat, which would allow you to sail regularly. Chartering is generally an expensive way to sail regularly. Joining a sailing club would be a good possibility too.
Unfortunately, larger catamarans are fairly expensive. Smaller cruising catamarans like the Gemini 105, Iroquois, or Catalac 8M are fairly affordable, but finding a slip for it may be a problem. Also, from what I've been told and read, the Med can be fairly challenging compared to some other places, like the BVIs.
I'd also recommend you read this POST
to help you get the most out of Sailnet.
Catamarans have some issues with handling compared to monohulls, often due to excessive windage, and the fact that they don't have a central hull to pivot around. Also, the technicques for sailing a multihull are slightly different from those used for a monohull.