We have 3 guys who can be added to the 60 Day IL to make additions to the 40 by opening day: Murphy, Perales and Penrod.
As of now, assuming Abreu starts the season on the 10 Day IL, and no prospect makes the 40 or 26, our bench might be Yoshida, Romy, Narvaez and Grissom. That leaves just Sabol (C) and Sogard (UT) as position players on the 40 in AAA. (Jh Garcia will likely start in AA.)
We will almost certainly be adding 2-3 position players to the 40 for opening day and 1-2 might make the 26. I doubt any prospect is added to the 40 and not the 26, so that is one key component to who is chosen. Team years of control might be the deciding factor, if it's a close call.
I could see us adding Thompson to the 40 and 26, and starting Grissom in AAA. We may hold off adding others to the 40 (and maybe 26) until we know more, but Eaton's ability to play multiple positions might give him the nod. I doubt Toro is an option.
I'd love to see a prospect or two make the 26, but it's looking less likely, unless a new injury occurs.