postgresql backups

hi friends,
we are going to use postgresql and we have some doubts about it.
1) How to backup Large objects, because pg_dump will not backup
the large objects. Can anybody help with some examples ?

2)How big is the database that postgresql can support?

3)How to change the size and datatype of a column in a table.
Because, no where in the documentation it is mentioned.

4) Up to which point can the data be restored? Is it upto the
point of
backup taken or upto the point of system crash?

5) How many connection does it support at a time?

6) How can we implement the database replication in postgresql

Thanks,
chava