I can contribute a little...
A. Before coming 'down' here... visit a travel medicine doctor or specialist in Tropical Medicine. Most university hospitals will have this type of specialist. It was not only good for my health, but also piece of mind. We discussed where I would be as well as lifestyle; so we went with Hepatitis 'A' shots (two...around 6 months apart); a tetanus shot, flu shot, Typhoid shot, and I highly recommend a Shingles Vaccine. I had Shingles here and they didn't know what it was. Not sure if that vaccine is here yet... but believe me you don't want it. Probably GOOD to be up-to-date on your Covid protocol. Some countries in Latin America require you to get a Yellow Fever shot... but most of those are situated partially in the Amazon... or other wetland type environments. ALSO... know that Dengue Fever is on the increase across the planet... and CR is no exception. There is no vaccine; but religiously applying some 'OFF' on the target areas (ankles, neck, ears, etc) before you start your day is important. Especially once the rains have started and water is starting to 'build up' and 'sit'.. just a tiny bit inside a hollow coconut shell is enough for a mosquito to lay eggs. YOU DO NOT WANT DENGUE. It comes out of nowhere... and you won't know what hit you ... even if you pass out face first on the bathroom floor and break your nose and collar bone (been there!)... you will be so delirious and feverish and 'ill' that you won't have to capacity to determine what is wrong with you. I have since grown citronella plants around the perimeter of my house; and I regularly cut some of it and cook it in boiling water; strain it, cool it, and spray it around. Easy. Smells better than a Costa Rican hospital. And recuperation took a few months and I'm guessing, the whole ordeal took a few years off my time clock.
B. This info came from my Tico friends that have lived in the countryside for their entire lives... Once a year they visit a pharmacy and get an Anti-Parasitic dose (2 pills usually; now chewable)... which I have now done for 5 years; every May 1st which is the unofficial start of rainy season. Easy to remember. Your 'gringo' body might not be ready for what the tropics has in store for you.
C. As far as 'general' health... I knew immediately that my 'diet' was changing... as eggs here are cheap and plentiful; along with the 'fat' on meats which is generally 'trimmed' off.in North America, but not so here... so, I took up WALKING every day... 4x a day... easy to fit into a retired person's schedule... especially if you have a dog. Big benefit from that is meeting the locals and getting the exercise as well as exploring your new surroundings. I tend to stop and ask people living along my route about plants and such, and have become part of a network, or sorts, where we all share seedlings; cuttings, produce overages, new things, etc. My sister, while visiting, couldn't believe how many times I walked out into my own garden to cut something while I was cooking... herbs, teas, tiny hot peppers, fresh fruits, veggies, etc. Even 'Agua de pipa' for a refreshing drink of coconut water... which is 'supposed' to be good for the urinary tract.
Hope it helps a little.
Pura Vida