Welcome Rob and Manuela. You probably have a bunch of great experience from your
service that will relate to managing a boat. I've never met a sailor that admitted to being an expert regardless of the years of experience. The sea will always teach you a lesson. One of the biggest cautions that good sailors give newer sailors is
experiment, but do not get in over your
head - There are old sailors and bold sailors, but very few old and bold sailors. You probably will not have that problem. I agree with Don C L's advice to learn to sail on something smaller. You probably did not learn to fly on a high-powered helicopter, and you should not try to learn to sail on something very big. It's not the
danger part, it's feeling the relationship between
wind, sail, and tiller that are difficult to feel in a large
catamaran. A boat under 25 feet is a better teacher. Another bit of advice is get into a sailing club, yacht club or find a sailing friend locally. Put in your location, and we can make some suggestions.
As far as costs, they vary wildly (by factors of 2-3 x) based on location, and to a lesser extent on the boat and your experience. Your question is like asking how much are the payments and
insurance on "a car" ... how would you answer?