Is there a way to force users to fill in certain fields (such as address, custom fields, etc). Is that something the API is capable of?
I also am managing 4 locations for 1 customer. Each website has a preferred location which is a custom field. Can I arrange that if a client wishes to subscribe to a different location (i.e. He is on the Montreal website and wants to join the Ottawa mailing list) that the subscription can be redirected to the proper list.
Mat has written a handy blog post on making fields required in your signup forms. You can read about that here: http://www.campaignmonitor.com/blog/post/1766/making-certain-fields-required/
Sounds like you'll want to set up a preference center to allow your subscribers to manage their subscriptions, see http://help.campaignmonitor.com/topic.aspx?t=113