I agree with your locks. I am just not as reticent as you to picks the favorites at this point in time. Others will have different opinions. Others have no interest in guessing at this point.
I agree that the number of corners could be 4 or 5. Therefore, it might useful to consider that the players you list at corner are competing for one roster spot, the backup corner position.
I agree that Ihedigbo and Barrett are competing for the #4S/ST stud position. I don't see Ebner getting THAT roster spot.
Once the 2 positions above are filled, we have all we need for position players, except in the case of emergency players in case of 2 injuries. We would have 4 corners and 4 safeties.
CHOICES AFTER WE HAVE OUR 8 DEFENSIVE BACKS
Obviously the choice of #4 CB could influence the choices below. Either of the potential #4 safeties could be a potential #9 DB as a STer.
We are likely to have 1-2 addition DB/ST roster spots available. Also, one of these 1-2 positions could be used on a developmental player.
If we are nervous enough about our 8, we might keep a vet who can be both an emergency corner and an emergency safety.
If Belichick is confident with our ST's, I could see him making this choice.
SUMMARY
6 locks as noted
2 position roster spots with contenders noted
1-2 roster spots available for those who best fill needs not fully addressed
I think 3 of each are locks:
McCourty, Dowling, Arrington
Chung, Gregory, Wilson
I think Moore, Dennard, Allen, Cole are in a battle for one or 2 spots and there is no distinct favorite(s) among that group. I think separating Moore and Dennard is more speculation than reality that they have any leg up.
At safety, Id say the same for Ihedigbo, Barrett, and even Ebner, especially if the corner # is 5.