Here's my guess as of the end of the 1st pre-season game:
Roster locks in BOLD.
QB (2) - Tom Brady & Brian Hoyer
OL (8) - Trent Brown, Isaiah Wynn, David Andrews, Shaq Mason, Marcus Cannon, LaAdrian Waddle, & Ted Karras
RB (6) - James White, Sony Michel, James Develin, Brandon Bolden**, Rex Burkhead, & Jeremy Hill
TE (3) - Rob Gronkowski, Dwayne Allen, & Jacob Hollister
WR (6) - Chris Hogan, Philip Dorsett, Cordarrelle Patterson**, Matthew Slater**, Eric Decker, & Kenny Britt
Offense total: 25
DE (4) - Trey Flowers, Adrian Claybon, Deatrich Wise Jr., & Derek Rivers
DT (5) - Danny Shelton, Malcom Brown, Lawrence Guy, Vincent Valentine, & Adam Butler
LB (6) - Dont'a Hightower, Kyle Van Noy, Elandon Roberts, Marquis Flowers, Ja'Whaun Bentley, & Brandon King**
CB (5) - Stephon Gilmore, Eric Rowe, J.C. Jackson, Jonathan Jones, & Ryan Lewis
S (5) - Devin McCourty, Patrick Chung, Duron Harmon, Duke Dawson, & Nate Ebner**
Defense total: 25
K (1) - Stephen Gostkowski
P (1) - Ryan Allen
LS (1) - Joe Cardona
Specialists total: 3
Suspended: Julian Edelman
PUP: Harvey Langi
** = Core ST'er.
Note: Patriots.com has Duke Dawson listed as a safety on their unofficial depth chart. Interesting...