Question about the cluster command

Hi,

Can I cluster the tuples in a table like that:

group by company_id order by opendate desc

How do I create an index representing the above logic to use it with the
cluster command. Can I automate the clustering process to best optimize
my database performance and always get the data about a specific company
ordered by date as fast as possible (to generate charts). Does
autovacuum include reclustering?

Cheers,
Anton Andreev