Postgres Size-limit

Hi there.

First things first. I just want to say I've moved from Mysql to Postgres
  for alot of reasons. :-)

My questions:
=============

    * What is the limit my PostgresDB can grow to? 4gigs, 8gigs?
    * What sort of system I'am a looking at running postgres on?

Now here's a really confusing one :-)

    * Can just can't decide which OS to use here:

    FreeBSD or Linux

      Which OS would you guys chose?

Last question
==============

    * Where can I find some real good tests done on Postgres which will
      indicate:

    - How fast Postgres really works
      - Postgres and other DB compared
    - Database UPTIME
    - Speed and complexity of DB