Yes, all capabilities I am looking for I am now able to do. Thanks
OK, the step I was missing was Insert Record(s) from the right-click menu to add sub-messages to a parent message. All is good now and appears to be working well for both reading delimited files as well as creating them from scratch. Thanks and it looks just like what we need.
Update: I am able to edit a protobuf file that I created with the attached case.proto using a Java program. Once I have delimited protobufs created, I can use copy/paste functionality to create new case records with their associated embedded messages. I can then edit the fields in the pasted records. I would still be interested if there is a way to use the New Record functionality to create a complex message with sub-messages and repeating fields.
Editing protobuf with nested and repeating sub-messages