1. You can and should transmit your apps before all LORs are in. LSAC will send updated reports to the schools as they process the remaining LORs.
2. When I FedEx'd one of my LORs to LSAC, they processed it within 2 days of receiving it. I'm not sure why they place more emphasis on letters sent that way, but I got the idea from someone else who said they process letters very quickly when received overnight.