Advantages and disadvantages of more than one dbserver on one server

Hello,
I want to discuss a little bit about the following situation:
I only have one server for my databases.I had to develope on this server and
also had to manage several databases, so I can expect problems if I had to
restart postgreSQL, if I changed the logging.....
What do you think about this solution:
For each database I want to let run one server, and the different servers a
located in
/usr/local/pgsql-733-1 data-dir: /db/pgsql-1
/usr/local/pgsql-733-2 data.......................

Is this a good idea? What problems can happen? I compile postgreSQL only
with the --prefix flag. What things I should do?
Each db got his own user, like postgres1, postgres2 or pgsql7331,.......

I sometimes need to log everything, but this is maybe once or twice a week,
but I can't restart the server during the day.

Daniel