There is no specific prerequisite. I can suggest to pre-provision all the space needed by Postgress. Since it won't ever release its space (as you said, PGSQL isn't "VP aware") it's better to allocate all its space since day 0 and forget about it. 🙂
This will have also a little side-effect: response time may lower a little (you don't have the overhead of space allocation when you write to an area still untouched from OS perspective).