Thank you for the response.
Depending on the tag being read it but typically it has two read 12-16 characters.
I think maybe the bank of pro mini's might be the best solution as they will then be able to store the ids found and transmit back when available kind of acting like a buffer.
Perhaps the master can loop through all of the children boards and send a serial command, if the child has found a tag it can respond and send it back other wise return false and the master can carry on through the loop.
Is this something similar to what you have in mind? Could i connect all of the prominis to a digital pin on a mega board, or does it need to be a rx pin?