Update: The first rig is set up and is currently mining at btcmine.com We'll have the other 4 rigs up tomorrow. The stats on the first rig can be downloaded here: http://btcmine.com/api/getstats/020d055f94131c4b29baeca9915c7e04917bb18e/ .
I highly suggest you research Eligius. Their payout system is far more intelligent and secure, rather than trusting the pool operator of btcmine. They offer more transparency, which will cause a greater confidence in your business proposal.
Also, may I buy one share?
Why not point each rig to a different pool, that way if btcmine is having a bad day, less blocks solved. Not all the machines have a bad day.
Say point one to btcmine, another to eligius, another to bitcoinpool and so on.
How and when will payments be made? (i suppose at the end of each month?)