Hi, Els! I hadn't seen this forum publication, I've had pretty busy months here at work. Believe or not, we were the first Green Building Council in the Americas to have its annual congress online, as a result of COVID-19.
I'll research a little and provide more answers to you, though I think the answer that you found to Question#1 is really good and comprehensive... though I`ll look more in detail for the guidelines regarding individual national parks. Just additionally consider this official source of information: https://www.visitcostarica.com/en/costa-rica/statement-costa-rica-tourism-board-covid-19
Of course everything may change before March, especially as vaccination against COVID-19 starts and becomes more widespread, thanks to the Social Security System and the Ministry of Health.
Also don't hesitate to write directly to my e-mail for more information. If you want (and have time for it) I could provide advise also on other locations that are interesting to visit (and non WH-related).