My plan was not to link the TLCs directly with the max485s (sorry I realize my post was vague). I plan to have an atmega328 at each location which will interpret the serial commands sent to it by the arduino master through the max485, and then it would in turn tell the TLC at its location which LEDs to turn on. So each node will contain a atmega328, a TLC5940, and a max485 plus (crystal, resistors, pins etc).
I only need to tell the slaves what to do and do not need them to talk back to the master so half duplex should be fine right? The whole reason for me going for this node based approach to begin with is to cut down on the wiring needed.
Please tell me I have not misunderstood this whole thing, I have a pile of chips on order 
Thanks for you help guys, the bit about the clock speeds really shed some light on a bunch of blank spots I had in the way these pieces interact.
-Sathi