Great questions. Unfortunately, unless you are a permanent resident, which you can obtain after three years as a temporary resident, married to a Costa Rican, or the relative of the Costa Rican (even your own child born in CR), you are by law not allowed to work, even in your own business. If you have a business, you can take on a superior or manager role but can’t do actual labor.
Do some expats skirt this law? Yes, plenty. But there are some big risks involved, like deportation.
The other issue is that labor costs are much lower in CR, so you probably wouldn’t make the income you’re used to, even for skilled work. Plus, with workers you’ll have to pay part of their Social Security, worker’s comp insurance, and other
You can start a business, even with a tourist visa. You’d probably have to go 45 minutes inland to Santa Cruz, which is kind of like the “county seat” of the area and where government offices are located. There you’d get a business license and register with the tax authority for income tax. That can be a process but it’s doable. You might consider hiring an accountant or attorney to help you with the process, especially if you don’t speak Spanish.