Use split and join

[Colin]

You can use a Watch node to tell you whenever the folder contents change, that will give you a message each time a new file appears or an existing file is changed (I think, though I haven't used it in exactly this way).
If a new file is added to you want to action just this file or re-do the whole set of files again? Your description suggests the latter but that seems odd.
Whichever is the answer then you need to send a set of messages with a filename in each one on to the next nodes which process them accordingly and once complete will delete the file. So no need for a loop.