Not sure I understand entirely, but let me try...
1) Fields are linked to Departments. Similarly, EPTs may be linked to Departments. Hence, if you have Field A assigned to Department 1, and EPT A assigned to Department 1, then Field A and EPT A are linked.
2) You can populate project fields in the template before you save it as a template. As a result, when you select that EPT, the field is already populated.
Andrew Lavinsky [MVP] Blog: http://azlav.umtblog.com Twitter: @alavinsky