All depends your environement and the admin tool that you have.
For example, if you are using cPanel, you can create different DB and also assign several MySQL user to a same DB.
To reduce potential MySQL privileges problem, it is easiest to have a same MySQL user for several DB. So that you just have to change the DB in Jms Multisites and the copy of the DB will be performed with the same MySQL user.
So you could have a tmplate rule like
Select the template site = <master_db>
New DB name = a rule that could be computed based on site ID (ie. db_{site_id} )
New DB user = empty (if you are using the same MySQL user than the master db)
New DB psw = empty
New table prefix = {site_id}_ In general I recommend to have a specific table prefix (event when using different DB - just in case where you are doing a mistake and write in wrong DB)
When you have the rule, you can use it in "manage site".
If you want to see some sample on how the JMS Templates is working, see our tutorial video 13, 16, cp-05
www.jms2win.com/tutorial