Traca will give you the definitive answer but I think biscuits really don't
reheat well (from my experience with leftover biscuits) and are best (as anything is ) fresh out of the oven. I think you could make the biscuits and refrigerate and bake in the morning.
We buy Mary B.'s frozen biscuits and they are absolutely wonderful--can't be made any better. (But it IS that brand, sold around here -south)
Since you are dousing in good gravy yes bake them the day before.
And yes to making the gravy ahead as well. If you were serving the biscuits with butter or honey or something they would still be okay but not as good as fresh- but you are making biscuits and gravy so go for it!