Any advice would be appreciated.

You're projecting this onto walls. Is the artist going to be projected too or just the art?

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.

I Think I have a picture of this in my mind. But to pull it off, what I would do is, have the artist do everything using a wacom tablet in airbrush mode, and a suitable painting program, and a screen recorder program. This generates the movie of the painting being done, step by step, without the artist in the shot, and no need for green screens or stop-motion capture of a real wall. If the artist makes use of a lot of masking tools, this may present a problem, I dunno.

Next I would go hat in hand to the live and stage COW forum and ask those guys, who are real experts, what setup to use for the synched projection. My guess is they would suggest Wings, Avstumpfl, or watchout, along with the proper video cards and computer setup, and the project parameters to make this a single aftereffects comp spanning all four projectors.

Finally, the artist rehearses in front of the projections (to a locked in music track would make it easier) to synch their movements with the recording. The playback then looks like a real-time event, "painted" with light.