There is only 2 Master Detail Relationship allowed per object and it can have upto three custom detail levels. You can read more about it here. I think total 40 Custom Relationship both lookup and master-detail. If any one is sure about the no. of relations then please confirm and share. Salesforce, Administration, Difference between master-detail relationships You can define master-detail relationships between custom objects or You can define a relationship between any two objects, standard or custom. . View Setup Audit Trail in Salesforce · The Dreamforce '15 Ultimate Content.
I presented the following solution at Dreamforce 16 at the MVP Process Only related records that have a master-detail relationship will be deleted Identifying these child records for cleanup purposes may become difficult.