Unless you are occupying four places in line the entire time, to me that would be "cutting", especially when your place in line may determine whether or not you get a particular item.
We open presents first, then have breakfast. The kids usually don't each much on Christmas morning anyway; I let them indulge in whatever treats they find in their stockings.
I hide everything in the basement. I keep a list for each kid of what's been bought and how much I paid for it. I use special tags for their Santa gifts and write them in very fancy handwriting.
It usually works out to be around $200-$250 per child (we have 2). We don't set a dollar amount, we just get them what they want and/or what we want them to have.