Jamie, Orpingtons are a great breed (that's where the Australorp comes from.) We currently have 16 hens, down from 20 due to old age. We keep our hens even if they aren't laying all that much, due to our tender hearts and the fact that the hens are just so darned entertaining!
Six to eight is a good start. If you order, you will have to order more than that--coming through the mail the chicks need to be kept warm, so a bunch of them are packed into the box--not all the breed you ordered, although you will have six to eight of the selected breed. The others will be whatever the breeder has as an oversupply.
May I suggest that you locate a local feed store, and see if they supply chicks or know of a poultry supplier. If not, I agree Tractor Supply is not a good source.
Our "start-up" flock was a dozen chicks. You have to expect a certain mortality rate. Chick death is not your fault--even the ones raised by the mama hen don't all survive. If you have a rooster in the batch, you need to decide if you want to have fertile eggs that can become chicks, or if you just want eggs you don't have to candle to see if they are fertile or not. We banish roosters to a friend's flock. For some reason she wants roosters!
I suggest that you get a copy of Chickens in Your Backyard by Rick and Gail Luttmann (ISBN0-87857-125-6) which covers almost every aspect of raising and enjoying chickens. We have had chickens for eight years, and I still refer to this book frequently.
You are going to have so much fun!!!