Even custom BP classes are procedural? Impressive! 
I bet it creates an organic experience. I was struggling to create procedural missions, because it demands a good enemy AI. Then I gave up the idea and stuck with a linear game like Kane & Lynch 2 (prioritizing the player strategy and smoother controls). So, even with the Marketplace stuff help, I know what you’re doing is extremely hard. I tried something similar and failed haha
I’ll be following your progress for sure (I remember you from UDK forums btw ^^)