Databases vs Schemas

I am seeking advice on what the best setup for the following would be.

My company provides a hosted web calendaring solution for school
districts. For each school district we have a separate database. Each
database has 57 tables. There are a total of 649 fields in those
tables. Here is a table of the different kinds of field and how many
there are:

time without time zone

bytea

date

smallint

boolean

integer

timestamp without time zone

numeric

text

9

4

8

1

79

195

36

8

309

Over the next couple of months we will be creating an instance of our
solution for each public school district in the US which is around
18,000. That means currently we would be creating 18,000 databases (all
on one server right now - which is running 8.4). I am assuming this is
probably not the best way of doing things.

I have read up on schemas and it looks like a good change to make would
be to create 1 database with 18,000 schemas.

Would that be a good idea? What sort of issues should I be aware of
(administrative, management, performance, etc...)? Is that too many
schemas to put into 1 database? What are the limits on the number of
databases and schemas you can create?

Should I try to re-engineer things so that all 18,000 instances only use
1 database and 1 schema?

Let me know if you need any more info.

Any advice and information would be greatly appreciated.

Regards,

Scott Otis

CIO / Lead Developer

Intand

www.intand.com