You really don't need 2 databases for only 10,000 users!
What is the requirement of having 2?
If it is just for redundancy then you are better off having the SQL clustered.
If it is for disaster recovery you can just keep a backup and recover very quickly from complete failure to a new SQL server.
It is not critical to keep the DB available as the clients will continue functioning without the SEPM and DB.
They just wont get definitions from the SEPM and you wont be able to do reporting or policy changes.
So you have this sliding window of risk where the clients becoming more and more out of date.
If you know what you are doing and have practised your DR process you can can recover the SEPM in 30-60 minutes with a DB backup.
Even if you don't have a DB and need to generate and drop new sylink,xml files you could fully recover your fleet of 10,000 in a day.
Adding additional databases should be avoided unless there is a very specific requirement.
Check the following:
http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/c68d849449ab97328825733e0069a691?OpenDocument