Will the Burnin Mining rigs plug and play with MinePeon and the stock CG Miner or do we need a special version?
Yes, plug & play. There is additional option (voltage regulation) not yet supported by stock CG Miner, but you probably won't need to touch it at all.
Also, is it better to place orders sooner rather than later to reserve the board or does it not work like that? (I'm in SebastianJu's Batch 6 order, very helpful guy btw.)
You have the answer to this question in the OP.