I think 10 DBs is a good number, though it could easily be 11 or 9, depending on other roster moves.
At Cornerback, the top trio entering the season will be Aqib Talib, Kyle Arrington, and Logan Ryan. When the Patriots go to nickel, Arrington will probably jump to the slot and Ryan will be on the outside. This arrangement is only because Dennard has missed nearly all of camp and preseason games, and faces potential jail / suspension. Until his status is determined, he can't be any higher than #4 in my eyes. If he is cleared, he could definitely start alongside Talib again, assuming he's healthy. He has the talent.
For the #5 CB, Cole looks like a safe bet. If the Patriots want to keep a sixth CB, Morris and Green are good candidates already on the roster, though I think it would be more likely that they swing a trade / sign another cut.
At Safety, Devin McCourty is locked in at FS and is a potential Pro Bowler. SS is a huge question mark. Last year, Gregory manned the spot next to McCourty. There was some good and bad, but it seems his bad were more blatant and obvious than the good. The team signed Adrian Wilson, yet he hasnt shown much in any capacity. Duron Harmon and Tavon Wilson are 3rd stringers at best, and should be primary ST contributors.
If I had to project the starting Secondary:
Aqib Talib - Adrian Wilson/Steve Gregory - Devin McCourty - Kyle Arrington
Gregory and Wilson would rotate depending on situation.
