Forms :: Force Users To Enter Data

My database is tracking Job/Project information. The users must assign the Job Contacts which can be both internal and external (ie: Contracts is a Client Contact, while Engineer is an Internal position)..

tblContactTypes which defines each of the 10 types of job contacts.
fldTypeID: fldTitle fldClient fldInternal
1 Contracts True False
2 Engineer False True
3 Other True True

The Job Specific data is stored in tblJob_Contacts

fldJobID (PrimaryKey)
fldTypeID (from tblContactTypes)
fldEEID for Internal Contacts (from tblEE)
fldContactID for External Contacts (from tblClientContacts)

My question is this...How can I force the user to enter the Contact information for Contact Types 1,2,3, and 4 while leaving the remaining contacts types as optional?

I would like a form with combo boxes for the first four Contact Types which must be assigned for every job and then a continuous subform where the user can assign the remaining contact types if needed.

Initially, I planned to store the first four Contact Types as separate fields in the main table (tblJob) - however, distribution lists are needed and it makes more sense for all the contact information to be stored in the same table.