The best thing we did in Cuba was rent a moped and spend two days riding around. I saw all sorts of things I never would have otherwise.
Another good thing we did was walk old Havana, just walking around and diggin it and taking pictures.
The buses are pretty good transportation, though they take awhile like any bus does. Except for the moped, I found traveling about to be pretty tiring. My wife has pretty good Spanish, even so it was often hard to figure out was was going on. One could hire a cab if he had the money.
I read a lot before we went about how there wouldn't be a lot of supplies (toothpaste, toilet paper etc). Did not find that to be a problem anywhere we went. Things I would bring if I went again: salt, pepper, picante sauce... anything to make low-quality, bland food taste better. Maybe some bisquick, peanut butter.
I didn't stay at low-ball places, it just seemed like the ingredients were low-quality (gristle in the ham, stale bread, greasy chicken) and the food preparation was less than inspired. Some places were better than others and some dishes were pretty good, just be prepared to make due. Bisquick and jam. and picante sauce.
the mojitos, on the other hand were beautiful. So were the cars, and the island generally was fantastic.
Lots of people with a hustle, some very aggressive. I didn't feel unsafe, but I had to get pretty assertive a couple of times to get rid of a hustler.
Lastly, the Peso, Cuk business is a real hustle. When we were there the money exchange places would only sell cuks and pesos, but would only take dollars/euros/Canadian/etc - no pesos for cuks. At the airport when you leave there will be a fee payable only in cuks (I think it was fifty) and they won't give change and the exchange place will not buy Cuban pesos.
It's like buying tokens at the arcade except they won't take them back when you leave, and not all the games use them.
So that's my advice - bring some strong food seasoning, rent a moped, don't be shy with the hustlers, watch out for the Cuk gotchas, drink Mojitos.