Hello Daryl,
I’m not sure exactly what your use case is, you cannot define an enumeration model object from a table as the enums are hard-coded.
You can use tables as enumerations when associating objects (I believe this is what you're trying to achieve) see Reference selectors and Reference set selectors ( https://docs.mendix.com/refguide/reference-selector & https://docs.mendix.com/refguide/reference-set-selector )
As for multi-selection in one dropdown you can use the bootstrap multi-select widget ( https://appstore.home.mendix.com/link/app/2295/ )
Hope this helps