I have attempted to add a custom "Primary contact" field to cases relating to Contacts. The main purpose is to enforce requiring that every case have at least one contact associated with it.

The problem is that when you hit Select on that field to pick a contact the popup shows every contact in system, rather than only the chosen account's contacts (like normally adding a contact would do). What is the best way to enforce this relationship for the selection?

On a related note, if someone chooses a contact first (with no account selected), I'd like to automatically fill in that contact's owning account as the case's account. Is there any feasible method with the provided customization capabilities to accomplish this?

We're using SugarCRM CE 5.0.0f, in the process of migrating our MS CRM 3 setup, trying to replicate our current customizations (such as the above).