The DMX part is easy since you already have the software and the DMX USB Pro. The software is probably especially helpful in generating patterns, as it means you won't have to program them manually. Look at either the DMXSimple library or at Toni Merino's blog http://www.deskontrol.net/blog/en/author/toni/. Toni's code is centered around a mega (though it works fine on an Uno too.) The extra PWM outputs on the Mega give a little advantage as mentioned by DVDdoug. Really all you need for a DMX shield is the connector and a MAX485 chip (and I recommend a 0.1uf capacitor).
Probably the most challenging part will be deciding how the DMX channels get to the strips and what will be sourcing all of the current that the strips will need. Using Mosfets will probably be the best option.
What is your time frame?
Feel free to message me if you have DMX questions. I have built a few projects using the protocol.