Currently my databases are stored in several exFAT format external drives. I want to format them to the new apple file system (APFS). Will there be any issues doing that?
This shouldn’t be an issue for the databases but you could test this by creating an AFPS disk image, copying the smallest database to the disk image and opening & verifying the database.
Not the same situation, but I formatted by internal drive as AFPS when I installed High Sierra. Absolutely no problems whatsoever.