best way to manage indexes

what would be considered "best practice" for my situation?

I have a table *member*, with column *name *that I want to put an index on,
because it is searched quiet frequently. When I create my sql search string,
the name will consist only of alpha-numeric characters and be compared
against lowercase matches.

SELECT *
FROM member
WHERE lower(regexp_replace(member_name, '[^[:alnum:]]', '', 'g')) ~*
'search_string'
OR lower(metaphone(name, 4)) = lower(metaphone('search_string', 4));

is it better to create an index that matches my search?
create index member_name_idx on member (lower(regexp_replace(name,
'[^[:alnum:]]', '', 'g')));
What if we decide we want to allow more characters in the search later -
just have to remember to update the index?

do I need two indexes? one for both search parameters (regexp & metaphone)?

perhaps there is a solution that I haven't thought of. any input would be
appreciated!

Thanks,
Jamie K.