The wide boards definitely shorten the learning curve. However, most people never sell them for that reason, so the used market is sparce. Another possiblity is to get a wide SUP with a mast track and use that for dual purpose.
As soon as you can comfortably cruise, I'd recommend getting a harness. You should try to sail where there are lots of others, like Cass Lake or Stony Creek. Also, there's a guy at Cass who occasionally gives lessons.