Sure, it's a simple, stable and performant database and it's ideal for small-to-medium Scoold deployments. I can't recommend any particular DB because they all have their tradeoffs. Simply use the database engine you are most familiar with. It is also quite easy to implement a DAO plugin for any database you choose, unless it it's already implemented.

For details on how to access the H2 DB in ./data and how to back up/restore it, read the Para H2 documentation.