How much disk space should my DB take?

In the recommended configuration, the DB only stores artifact-metadata, build information and properties. The "indexed_archives_entries" table for example, stores the information required by the class searcher. As a general rule a database will take about 1MB of space for every 100 artifacts, but this varies based on the database, the history of the artifacts, the database settings.  This also assumes that the actual binaries are being stored in the filesystem (recommended) rather than being stored as blobs in the database.

if you don't need archive indexing it can be turned off and save more space.

For example:

USE <your database name>

EXEC sp_fulltext_database 'disable'

You can find more information about turning off archive indexing here and here.