Do a search on Ginnie Springs and Devils Den both good places for open water
divers that are in the area you are looking at.  Crystal River is ok but not
much to see.  Also Rainbow Springs is a nothing trip in my book.  If you
want to snorkle with the manatee you have to come here in the dead of
winter.  The manatee only come to the springs to get warm in the 72 degree
water.....that should give you an idea of how cold it needs to get for that.
Ginnie Springs should give you a good North Florida dive trip.  Bring a dive
flag and put in at Devils Ear and drift down the Sante Fe River to Ginnie
and then get a taste of cavern diving in water that looks like windex.  Just
my two pennies.

steve