Hi dmease729 this depends on your environment and on how many computers are managed. After installing, without any agent-to-server communication yet, the database and transaction logs should be at less than 100 MB
Disclaimer: These numbers may be a little unrealistic.
A completely clean install of ePO 5.1.1, with no automatic product checkin, and before running any software manager operations, gives a DB size of approximately 30MB.
The first time a database snapshot task runs, this increases to approx. 500MB.
These are pretty much the bare minimum, as any other operations will only increase the size of the DB.