Here is a good video on the process, doing what you intend, only for
Central America. SAS planet isn't a site to download charts, it is a site to build custom charts. Warning, it is very time consuming, and requires a fast
internet connection. Like, for a significant area it might take a month.
If you are lucky, someone will have already built charts for the areas you are interested in and share them with you.
Navionics on an
ipad might be acceptable, not 100% accurate, but good enough that if you sail in daylight you would be ok. And much easier to get charts for. They might be out a mile or 2, but if in daylight if you can see land you can
work with that.