can Multi-DB use less than 16 databases? Would i benefit from this Multi-DB? How else can i speed up

we have a huge database (several Gigs) on our two sites as it is a newspaper, would i benefit from using Multi-DB

How else can i speed up my site?

I have a limit of 10 databases 5 of which are being used 1 of those 5 is my wordpress database. I have created 5 databases for use with Multi-DB what do i do?