Apoc.periodic.iterate - running multiple instances

Basic question around using apoc.periodic.iterate - are there reason/concerns with running various threads that iterate through a load function. All that's working great. My periodic.iterate over the target file is pulling 10k at a time and moving along...bit like a snail, but that might be my machine not apoc.

But wondering if there's a reason not to run say 3 or 4 parallel runs of this load as I've about 6 files to go through. There's the concern of the "horse/cart" issue - not having a node to connect to in say in File B when the desired node for File B's node to connect to, is in File A. Will periodic.iterate "wait" or just fail? Or worse, will I be left not knowing that certain connections ("edges") are missing.

My questions around best practices. Maybe there's a "clean up" query that allows for faster uploads for large-scale inserts.