You said that you want to have many databases to simplify maintenance.
I'm not sure that I understand that. Especially with regards to change
control. With multiple databases you run the risk of one or more
databases becoming out of sync, either intentionally or
unintentionally. This can turn into a real headache if you aren't very
careful.

Also, will you ever want to research information on your customers as a
whole? You didn't include any information as far as what these
databases actually hold (this would have been useful to know), but
assuming that they hold sales data as an example... if you wanted to
find your total sales across all customers then you would have to
select across many databases. If you got a new customer you would now
have to change any queries that select across these databases to
include the new database.

Good luck,
-Tom.