Maximum Number Of Databases

Databases per instance of SQL Server = 32,767 (http://msdn.microsoft.com/en-us/library/ms143432.aspx)
The total number of databases on a particular server is not all that relevant. What is important is how busy each of the databases are (and to a certain degree, the size of the databases in relation to the size of the available disk space).

If you will be setting up one or more new SQL Servers, determining how many databases should be on each server is not an easy task as you probably don’t know what the load on each database will be. In this case, you will have to make educated guesses on database usage in order to best distribute databases among multiple SQL Servers to get the biggest performance benefits. And once you get some experience with the databases in production, then you can then move them around as appropriate to balance the load.

Delete A Database

To delete a database no-one must be connected to it (or the delete will be refused)
In SQL Server Management Studio right click the database and select delete.