Hello soboyle, I'm not sure that I can be of much help, since conditions on my trip were incredibly mild. It hovered from maybe 20 to 32 degrees F, so really not bad at all. But I will happily share what I know.
Clothing wise, I went with many light layers, including wool base, down and synthetic mid layers, and then waterproof outer. But this is such a personal choice. I started with what I knew worked (such as wool base) and built from there. I relied heavily on the Antarctica XXI guidelines that were provided to us. I tested everything out ahead of time, too - donned the whole kit and went out walking in sub-freezing temps. I had everything I needed and never felt cold or ill-prepared. My polar buff was great, kept my face toasty.
In terms of camera gear, I rented a second body identical to mine, and set up all the menus to be clones of my regular setup. This way I could work with two bodies at all times, seamlessly. Switching out lenses was minimized, too, which I was advised to do. It worked beautifully, although it was heavy (for me, anyway). I did bring a tripod, but barely used it (although I was glad I always had it as an option). No failures. No battery issues. No regrets in terms of what I chose to bring with me. I used most of my weight up on camera gear and re-wore and rinsed clothing. The gear was way more crucial to me than clean clothes, lol!
In terms of backup, I went to town. I wrote to dual cards in camera, then after every excursion, I downloaded to hard drive and external drive. I had 4 copies of everything. Never deleted anything from the cards. Lots of insurance!!
Hope some of that helps you out! It's a tough process trying to decide what to take. But nobody can really tell you, you just have to figure it out. That was my experience, anyway.
Good luck to you!