I was going to mention Williams until I saw rammmer mention him. He'll have an impact, immediately, if they choose not to RS him. (I don't think they'll even consider it.)
On the OL I don't see any mention of Alfred McCullough or Tyler Love here so putting Aaron Douglas in the mix—starting at that—doesn't pass my logic test. Boswell and Steen are two to watch this spring as well. Not to replace starters mind you, but to see how many different positions they practice at this spring.
I'll be watching Chris Underwood this spring as well. He's one that needs to "make his move."
FWIW, in our rotation last seaon, Brandon Gibson was backing up Julio. He's another to keep an eye out on.
Bottom line, when it comes to our offense, the LT position is really my only concern.