Hi, I love Hemingway too. Almost an obsession. Visiting Cuba, you might get a feel for why he liked the country so much.
Now, about safety, I can say with 100% certainty that all of the areas you mentioned are safe. There will be some people who tell you to watch out or maybe they can name a single bad anecdote that they heard from somebody, but I say, it is safe, completely.
I have lived for months in Cerro, near the Plaza de la Revolucion. I’ve walked the streets day and night. The area has a bad reputation. There are dogs in the street sometimes broken bottles, but never once has anybody every even approached me to ask for money or anything. The most trouble I got was from a small dog barking at me once. In my opinion, there is absolutely no reason to be worried about walking around in this area. And if somebody ever comes up to you and notices you as a tourists and starts chatting you up (a clear sign that they are just setting you up to ask you for some small change), just continue walking, without responding. They will lose interest right away.
Casablanca/Cojimar/Regla is just as safe. Even on a busy day there will not be many people there. In the summer especially. It will be hot and humid. You won’t be hassled by anybody.
I will say, safety in Cuba is a top priority for the government. It is extremely rare for tourists to have serious safety issues. The street beggars and restaurant scams are the biggest concerns, and even if you are completely blind and fall for those things, the most you will lose is a few bucks.
Assaults, robberies, things like that… you would really have to try your best to get into a bad situation for something like that to happen to you.
