DBs and Schemas

I'm looking for some input on a configuration I'm implementing.  The long
term goal is to providing hosting for companies and organizations with a
basic/generic set of applications that use PostgreSQL.

Most of these applications want to be installed in their own database.
Given I'm looking at 6 or so already this would be 6+ databases per
company.  Not my idea of an easy to admin situation.

My plan is to make one database (per company/organization) and modify the
installation scripts and the applications so they end up in and using
different schemas (probably named the same as the database would have been
named.)

I currently see see several issues.

1. Modifying the applications to use schemas instead of connecting to
   specific databases.  Getting the authors to use schemas so I do it
   once.

2. PostgreSQL usernames are global to the instance (?) not specific to the
   database which means each username has to/should include a grouping
   type of prefix/postfix identifier.  I think this is so.  Please tell me
   I'm wrong!

3. Isolation of users in a database from other users of another database.
   (Grants, groups, etc.)  Just making sure I do it and not cutting them
   off from system stuff they need.

And several more, I'm sure.

Most of the reading I've done so far hasn't got into this very deep. (What
did I miss in this arena?)  I have done this type of setup before many
years (10+) ago using Oracle but think there are significant differences
in their way and the PostgreSQL way.


TIA,
Rod
--
    "Open Source Software - You usually get more than you pay for..."
     "Build A Brighter Lamp :: Linux Apache {middleware} PostgreSQL"