I would offer the opposite advice from that given by Cary. Avoid all-inclusive hotels at the beach resorts: you could be almost anywhere in the tropical world at one of those resorts, you will not get any idea of Cuban culture, and overall they are really quite horrible (disclaimer: I absolutely hate all-inclusive resorts, and I hated Veradero -- I went there for one of those silly "destination weddings". The village was okay, but rather dull. I escaped to Havana as quickly as I could!).
Definitely plan to spend much time in Havana! It is an awesome city, vibrant and exciting. Just go for a walk in the evenings, and you will hear the most wonderful live music coming from almost every restaurant/bar. And, there are so many restaurants, the fun is in trying different ones (rather than eating the bland swill offered by all-inclusives, not to mention the watered-down drinks). Paella is a national dish (a spicy rice and fish dish), and you must drink a mojito (white rum with mint and lime!).
There is so much history in Havana, so much wonderful architecture, and it is a very safe city. It has been about 10 years or so since I was there, so I can't recommend any specific place, but I did have great fun one day being driven all over the city in a "coco-cab" (which is something you must do in Cuba!).
Oh, I just saw your new post. I was not yet playing guitar when I was there, so I can't comment on workshops, but most live bands -- a lot of Cuban latin-jazz -- have a guitar player or two. As for currency, they happily accepted US dollars almost everywhere I went, although they have their own Cuban dollars. It is easy enough to change money to the local currency, particularly if you have US dollars. It is not particularly expensive. It is a fairly poor country, probably better now, but you will see a lot of poverty and things are a bit run-down here and there.