Again, I don't have some sort of step by step solution for you, I was just trying to share some thoughts.
I would probably create a new list that I would use to track when an email had been sent for a "batch" of items. I would probably try to find a way to group the items logically, so I knew which ones were a batch - that is, I'm assuming that on Monday you might add 10 items for John Jones, and want to send a single email, and on Wednesday, you want to add another 15 items for John Jones and send an additional email. Is that correct?