I'm a big fan of GRK-Fasteners. I would use these: http://www.homedepot.com/p/GRK-Fasteners-9-x-2-in-Star-Drive-Bugle-Head-R4-Multi-Purpose-Wood-Screw-330-Pack-101099/203533441
Length is somewhat dependent on how many layers of subfloor you have, but I wouldn't use anything less than 2"..
No...