do you have to brine a fresh bird?

The dry brine method I use here is easier, I've found, than basting during the roasting, especially at very high heat. I have not ever tried this method (spatchcocking, then roasting quickly at high heat) without doing the salt brine, so I cannot say for sure whether you will be happy with the results, not brining. I've read that 24 hours of dry brining is the absolute minimum. ;o)

You absolutely don't. A brine provides an extra layer of moisture, which can help the turkey stay juicy when cooking, but this can be addressed with basting and a covering of foil. Just make sure you're seasoning the bird well before roasting!