Hi Ernest,
The most I've ever done is 8 racks of spares. But, I know I've read threads of people doing 12 racks of BB. Do a search for "12 racks" or similar and you will find some info.
Yes, you will probably use more fuel. I'd just load up the ring and be done with it. Shut it down when you are finished and reuse the leftover charcoal on some other cook. Then you won't need to worry about refueling in the middle.
You will also come up to temperature slower, if you are doing minion, start off with a few more lit than usual. This can affect your cooking times too, so take notice of that.
And also you will probably need to do some rotating because your air flow is probably not going to be as good, especially if you have a bunch hitting the edges of the middle section, and that can cause hot/colder spots. No biggie, can be done. Have fun.
Todd