The Referee section has guidelines for quickly putting monsters together, but no official bestiary is planned. That said, almost any OSR bestiary will work. I personally use the Monster Overhaul, but if you want a free one, the BFRPG bestiary are also excellent.
I think the only major difference is the Unified Save, which is based on HD. That *will* be on the Rereree Screen I'm hoping to make.