I loved Cuba, stayed at two different resorts (in Varadero and Cayo Coco). For comparison I've also been to three different all-inclusives in Mexico and DR. I found the staff in Cuba far superior in terms of friendliness and professionalism. You also won't be harassed multiple times per day to buy a time share in Cuba, which is what happened in Mexico and DR. As a matter of fact we couldn't even leave the airport in Mexico without that happening!
You will need to know about the currency exchange at the time so ask your
travel agent or someone in the know, keep your tourist visa card in your passport so you don't lose it! You need proof of medical insurance and check about electricity at your resort as you may need a converter to plug in your devices. The water is safe to drink and the resort districts are safe to travel in. For all -inclusives in general go to the orientation your travel provider gives and only book excursions through them, for the safety of your credit card and reliability of the product.
The beaches are fantastic, entertainment and food are resort specific so maybe find a message board dedicated to that resort location and ask questions. I thought the local fruit and dairy offered was awesome. We had a fresh juice bar and a made-to-order omelet station at breakfast, and a made-to-order pasta station and grill for supper every day, at the buffet. I think I ate my body weight in yogurt and ice cream as well, so good. And if you like higher quality booze you can ask for it by name and if they have it they will give it to you. The better quality stuff is kept under the bar and they make the "blender drinks" with the cheap stuff, but that is the same at every all-inclusive.
Take sunscreen, over the counter meds , and any personal care products with you as you may not be able to get what you want in the store on site, or pay a premium for it. But again this is true for travel anywhere, including Disney!