OK, here's a little starter info from someone who goes to Cuba often - I spent just over 2 months there in 2014 alone. You don't have to stay with any group or in tourist destinations as far as Cuba and its authorities is concerned; you can pretty much do anything that's legal. (If you are going with a group, of course they may have their own rules.) The exception to the "anything legal" is that you cannot participate in the highly subsidized stuff intended for citizens alone: you can't access the health system for free, your museum and concert admissions will cost more, you obviously won't have a ration card, and - the only annoying part - you must take 1st class busses traveling inter-city. (The reason this is annoying is that they don't go everywhere, but they probably go everywhere a first -time visitor without relatives on the island needs to go, so OK.) You can take public transportation within Havana even though it's subsidized and incredibly cheap.
There is essentially no violent crime in Cuba, even in Havana, compared to the US. The incredible feeling of freedom of being able to get out of a concert late at night and walk to the bus stop or anywhere without being afraid is one of the reasons I love Cuba. There is property crime though. Watch out for pickpockets and for purse-snatchers on bikes. Oddly enough, the poorer areas of the city are the safest. Since there are no tourists, there are no tourist- predators. If you can get past the Lonely Planet idea that the city is only Old Havana, Vedado, and Centro Habana, and find a place to stay in one of the 11 other districts of Havana, you will have a good time. You need to speak Spanish to move outside the tourist orbit, of course.
Finding stuff to do: check the Granma (newspaper). If you have internet access, the Cartelera Cultural comes out every week <email@example.com
There are 6 junior conservatories, and the National Conservatory (Instituto Superior de Arte) in Havana alone and all of them have guitar studies. I haven't permission to share anyone's contact info, but I would recommend showing up with a big handful of new strings and asking at the office if you can speak to one of the guitar professors. New strings are gold there. People like D'Ad hard tensions, but anything will be very gratefully received.
Oh, and you might want to drop by the Leo Brouwer office - Oficina Leo Brouwer - Calle E #517 apto. 13d, between 21st and 23rd in Vedado. They're putting together a new festival - voice, not guitar for Sept./ Oct. Make a contribution and stay to chat. This is also Editorial Espiral Eterna; you can get some sheet music.
Time to explore! Have fun. Don't worry too much.
The basic thing about playing the guitar is the pleasure you get from it. There's nothing wrong with pleasure is there?