Well...you would no longer need the level shifters (233's) on any of the boards, Master or slaves, unless you still plan on wiring them at some later point, because you will be feeding your RF module input directly from the PIC output pin, and obviously the receive output from the RF module goes back to your input pin on the PIC. However, you will need to do a little bit of thinking about how you syncronise your data and clock into a single serial stream. One popular way is Manchester encoding/decoding, and I would suggest that you carefully look into and understand that. It means of course that you will need to write a bit more code for the PIC's, but hey, it's all learning...
As for module selection, there is a vast number of different types available, spread over quite a few frequencies too. Given that you still haven't filled out your location in your profile, I have no idea what's legal and license free where you are, so I can't recommend anything specific.
Radiometrix make half decent transceiver modules across the range, but you may not be able to get them where you are, RF Solutions Ltd is another manufacturer etc...There are loads to choose from, so find something legal to use without a license in your country and all on the same frequencies.