Wow! Lots of comments! I'll have to read through them in a minute.
Cooked off my first batch. I filled a 12" cast iron skillet 1/3 of the way with Crisco, and brought it to 325ºF.
I drained the buttermilk/mustard mixture off the pieces, hit them with salt and pepper, and coated the pieces with simple flour. I placed the breast halves and legs on the outside radius of the pan, and put the thighs in the middle. Had to play with the heat to maintain my 325ºF (I used a simple spatter guard on top like Alton Brown uses which yields a crispy/crunchy crust). After the bottom and edges were a deep golden brown I flipped the pieces once, and cooked that side until it was golden brown. Removed to a rack over some papertowels to drain where I lightly seasoned the crust with some Kosher salt.
First things first, there is no way I would bother making a pan sauce. I have a well-seasoned pan, and the only things left in the pan were melted crisco and a few flecks of flour. I think a separately prepared veloute'/bechamel using chicken stock and milk fortified with some pepper/herbs/garlic and thickened with roux made from rendered chicken fat would be much better and practical.
The drumsticks were fantastic. The thighs were awkward to eat. The breasts were way too thick compared to the crust they had when compared to the meat/crust ratio of the legs/thighs. Alton Brown says the bottom deep-brown spot where the pieces rest on the bottom of the pan is viewed as the best part by many in the south. Personally I would have liked to have a uniform crust that a deep fryer would have given it. I'd also have more fat to dampen the temperature swings, along with an automatic thermostat.
I'm really not sure how much a difference soaking with buttermilk vs not soaking makes. I'm going to marinate 1/2 a chicken today in the same marinade (minus the tarragon which seemed pointless), and then reserve 1/2 the chicken plain. Tomorrow I'm going to try deep frying the pieces in my big 1gal GE basket unit rather than pan-frying.
I think I'll try something else too. Butterflied chicken breasts and thighs that have been boned. Then everything can be eaten with a fork except the drumsticks which are great to chow by hand. Everything will also have relatively equal thickness for that perfect ratio of crust to meat. Then simply serve the chicken/milk gravy over top the pieces.
Gotta' read the posts here and then get some errands done.