postgresql storage and performance questions

Hi,
I have a few questions about the storage and performance

1. How do you estimate the table size in postgresql?
For example if I have a table 'Dummy' with 1 varchar (40) & 1
numeric(22,0) fields and 1000 rows, what is the tablesize estimate for
this (including the row overhead etc)? How many pages will this
occupy?

2. Also if the table contains null columns, does postgres allocates
the same space for these nulls columns? How does it handle 'nulls' in
terms of storage?

3. How does oracle handle these 2 cases?

4. Does increasing the block size in postgres improve query performance?

Thanks in advance
Josh