I've not done this, but I PSMed Leonard Bernstein's Mass last spring, and just wrote blocking in my score. I've tried the whole slip sheet thing with the folded corners, and I just don't like it. My cast had 16 Street Chorus (soloists), 2 choirs, a boys choir, a ballet company and the Mummers, so similar in size I think. I just treated it as I would any other opera that I SM.
As for the score, I was given a bound copy by the producers, and i took a few hours to scan, crop and re-print for my own notebook. No digital copy of this score existed, so I actually created it for them.