Is there a way to limit the number of delivery line items that can be assigned to a delivery? Thanks
I believe this can be done in the data transport routine (VOFM routine -> Data Transfer -> Deliveries).
When copying items from order to delivery, there is a field LIKP-ZUKRL that can be used to split the deliveries. In the routine just count the line items and, after certain number has been reached, fill in LIKP-ZUKRL field. The counter will have to be stored in ABAP memory (because all the data inside the routine is initialized in each call) and cleared after each document. I'd definitely suggest to get an ABAPer to write the code.
Also there is some configuration for Subsequent Delivery split, but it works differently. First it creates a large delivery and then (i.e. subsequently) sort of spins off the smaller ones. But take a look - maybe it will work better for you.