2: Just clean it, lube it and shoot it. Mine was pretty dry out of the box.
3: No. Just sight it in. However, the M400 has an upper/lower tensioning device in the lower receiver. You will see it sticking up in the void behind the trigger, where the rear upper lug fits into the lower receiver. It keeps upward pressure on the upper receiver rear lug which reduces wobble/play. Mine came adjusted from the factory and my rifle has no upper/lower play at all. To adjust it you have to remove the grip and adjust it from the bottom with an allen wrench. Close the upper and lower and push in the rear pin. Then tighten the device until its snug and any upper/lower wobble is gone. Upper/lower play doesn't really affect accuracy, but it does effect consistency and getting rid of the play makes for a more solid feeling rifle, and reduces the cumulative effects of wear from upper/lower play.
4: IMO, it's not an optimal deer caliber. But a good bonded bullet should do the job if you do your part.