In TFS2012, the orgnization of collection and team project

Hi,

If I have many team projects in one single server, such as 500, should I put them all in one collection or in different collections?

If put them all in single collection, thousands members accessing the collection (database) in same time, does SQL Server instance degrade performance?

If put them in different collections,such as 5, does TFS consume more resource but higher performance?

Please ignore the issue of data isolation.