Newbie question PostgreSQL / Postgres Plus / Tuning

Hi,

Is there a difference between the standaard PostgreSQL en PostgresPlus from EnterpriseDB. We're planning to replace Firebird with PostgreSQL. We don't know what version to download: the one from Postgresql.org or enterprisedb.com

I heard many rumours that PostgreSQL out of the box is not configured optimally (please don't give me sermon, it's just what I heard J). We would use the database in a enterprise ERP system, with lots of Inserts/updates/reads. Approximately max. of 50 users. Speed is very important (of course). DB server should use all memory available for PG. Are there any things I can check to optimize ?

With Firebird, we had to do Backup/restore to keep the size of the DB in place. How about vacuuming PG ? Is that done automatically ?

Sorry in case I ask very basic questions.

Thanks a lot,

Nico