Hi Phi,

regarding System and Application data you cannot exceed but you can manage the usage and reduce it by deleting old versions of your code.

The database estimation is harder to be done, depends on the number of columns, data types of each and indexes used. Although not quick to be done, there's a few steps recommended to have an estimation of it:

https://docs.microsoft.com/en-us/sql/relational-databases/databases/estimate-the-size-of-a-table?view=sql-server-ver15

Regards