Welcome to the community, @Sandra_Southwick! :grinning_face_with_big_eyes: If you want only one of those options to be selected for a given record, that would be a Single Select field type. If you want to pick an arbitrary combination of options from a list, that’s the Multiple Select field type. More about these field types can be seen here:
Base limits are set by the plan of the workspace they’re in. Here’s an overview of the workspace plan types, and the base record limits for each.
Free-plan workspaces will always be free. There’s no time limit.
You can export any table from any base as a CSV file, though there are some limitations to what will be exported. Read more about CSV exporting here:
There are also third-party tools that will let you create more robust backups of your bases. I don’t recall the names off the top of my head, but a quick search of the community should help you find the related threads fairly quickly.