As much as you want to win the opener, there are 15 games after that to worry about. If Tuck has a bad neck, the Giants should sit him and not jeopardize the entire season. It looks like the Giants are thinking that way, since they signed undrafted rookie FA Trattou to the active team from the practice squad. To make room for him, they put Goff on IR. The fact that they waited a few days to IR Goff instead of doing it right away probably shows that they wanted to wait to see Tuck's status before deciding whom to activate. If Tuck was fully healthy, they might have signed LB Tracy off the practice squad to bolster the LB crew.
With Osi (and possibly Tuck) out, I would not rely on Dave Tollefson as the starting DE. Even if they do start him, he is not a great run stopper and he will not be able to go the whole game. I would slide Kiwanuka back to the DE slot, use more of the rookie LBs and perhaps more of the 3 safety formation on defense.
Redskins do not have a great defense, Giants offense should be able to move the ball.