Advice on index and constraint definition

Hi,

I have a table like the one below where all of the fields are foreign keys
except "prv_id" which is the primary key:

prv_id serial
prv_user_id inetger
prv_client_id integer
prv_customs_id integer
prv_patent_id integer
prv_doctype_id integer

a) I read that it is a good idea to add an index for every foreign key in
order to improve record management when selecting data for example.

b) I need to avoid duplicates in the combination of fields "prv_user_id,
prv_client_id, prv_customs_id, prv_patent_id, prv_doctype_id" so this
drives me to set a constraint with such a field combination.

Are statements (a) and (b) correct?

Respectfully,
Jorge Maldonado