After you've made a grid, a way to use that grid to automatically export each gridsquare as its own file.

Furthermore, a method to create new maps for each gridsquare as well (I know, resource intensive af)

As long as files are named A1, A2, B1, B2; Import as Grid should import files as backgrounds (under sea layer) and place them according to their names. With the examples you'd have a 2x2