Q: Is it possible to make User defined Fields (UDF) mandatory?
A: Yes, but not as default. But if you use the Item Placement Tool to move the UDF to the main window, then it is possible.
Q: Can you with mandatory fields set conditions between two fields, so if field A filled, the field B shouldn’t be filled?
A: At the moment it is only possible to have all fields mandatory or not, but please try the B1 Validation System; with that you can set up advanced rules and make your own validations.
Q: If I make a field mandatory on the main BP or Item window does it also become mandatory on the Quick Create windows?
A: No, this is technically not possible.