-F option, RAM usage, more...

I would be grateful if someone could help me understand exactly how
the -F option changes Postgres' behaviour.  I am trying to tweak the
speed at which it operates:

I understand from the docs that -F ".. prevents fsync()'s from
flushing to disk after every transaction.." and that this boosts
performance because RAM accesses are far faster than disk accesses.  I
have also seen some impressive stats regarding the degree of this
performance boost.

Some specific questions:

1. How often DOES PG flush to disk - if at all - when the -F option is
invoked?  Can this be controllled?

2. I have no first hand experience with Oracle, but I understand that
one of the keys to its speed is its ability to pull the entire
database (or selected tables) into RAM and work them from there.  Is
this comparable to Postgres' -F option?

3. With -F, does PG pull the database into RAM at startup?  Or does it
pull data into RAM as it is accessed.  (eg: the first few queries
would be slower, but subsequent queries on same data would be
faster...)?

4. Does the -F option speed SELECTs as well as it speeds INSERTs?

5. I have a dedicated Linux 2.2.16 db server with 2GB of RAM. How can
I be sure that Postgres is using all the RAM that it can? (-S
option? -B option?)

6. How does Vacuuming affect PG if it is running with -F?

Any other information regarding -F would be appreciated.

Thanks in advance.

Mike Biamonte