Hey @jmtichell – I’d recommend checking out this post on masspayments for more information/step-by-step guide on using masspayments in Dwolla - Mass Payments - Pay 5,000 People in Five Simple Steps
You can definitely use correlatioinIds in your masspayments for each item as well as for the masspayment as a whole. You can find this listed in the Request Parameters table within the masspayments section in our API Reference Docs.
It may also be worth noting that there aren’t any defined rate-limits in the API that would lock you out, apart from concurrent Balance sourced transfers (this isn’t currently supported).
Hope that helps!