Hi Aimee, welcome to the forum and Costa Rica
You don't have to become a Costa Rican citizen to live in Costa Rica, and you don't have to give up your US citizenship, even if you were to become Costa Rican one day. We have a good article on residency requirements and classes here:
Costa Rica retirement & residencyWhen you work in Costa Rica the easiest option is to get hired in your home country, the company will be able to obtain work permits for you and the pay will be better.
If you come here first, you can work "informally", or you can look for a company that needs your skills and can assist you in obtaining the permits. Good possibilities are teaching English at companies or working in a customer service center (like sportsbooks or software companies).
There are a few different Vista del Mar towns, what part of the country are you considering? (Central Pacific, Guanacaste, Central Valley, etc. ) I know of one on the east side of San Jose. This is a nice area, but you would need a car and would probably want to work downtown and not in any of the western suburbs.