Well, first, you don't *have* to make the entire bag, especially if you're making a bazillion other things. I wouldn't, but that's just me.
Stuffing doesn't expand exponentially, so I don't know what the bag is talking about. Sure, it might a little bit, but it's not like rice, or something.
If you put extra broth in, it will get mushy and you won't see the cubes.
You can mix the celery and onions in with the mix, you don't have to put it on top. Adding in the extra broth, along with some melted butter should keep it from getting too dry. Just keep it covered in the oven.
250 is awfully low. Is that what the bag says? It's going to take a LONG time to heat all the way through at that temp. I wouldn't do anything lower than 325.
Did I answer all your questions?
-m
Wife to Jonathan
Mom to Sophia 12/02 and Amelia 12/04