various questions on column sizes & cleaning up

We've inherited another linux postgres database project with many
tables.  We're trying to get a better understanding of the physical
disk space properties and requirements for this database.

(Nice trick:  running "select relname, relfilenode from pg_class where
relname not like 'pg%' order by relfilenode;" helped us determine
which table and index maps to which physical file.)

My questions:

- Is there a SQL command I can run to determine the actual size of a
row within a table?  (Or the byte sizes of each individual columns?)

- Is there a listing of the column types and the number of bytes
required?

- Does running vacuum clean up the indexes as well as tables?

- Or is there a different command we should also run for the indexes?

- Or is nothing necessary for the indexes?

Thanks in advance!

Stephane Charette