Glad to hear you've caught the UL bug! Just did an A.T thru-hike myself this year so congrats on your prep for 2013 - You'll love it! There are many more experienced people here that can chime in their advice (I contribute a large portion of the success that I had on the trail to the proper advice and preparation that BPL helped me get before I started my thru) Lots of options out there, but here is what I would do if I where you:
1) ULA Circuit (used an MLD Exodus and Burn on my thru. I own this bag, t will carry weight well and is light but good.
2) Trash Compactor Bag
1) REI Halo 25* (switch to MH UL 45* for summer) Ditch the STS Liner - I don't think they work very well. Adds 1 LB
2) Z-lite CCF Pad OR bring a Neoair Xlite w/ a 1/8" Gossamer Gear or similar CCF Pad underneath to protect it. Used a Neoair for 1,800 miles till it got a slow leak, and being to lazy to fix it with the repair kit I was already carrying, sent it hope and slept on a GG Torsolite Pad (3 oz.) with a 1 oz. foam hip doughnut. Neoair was more comfortable.
1) Lunar Duo is popular and should be great for you both. Ditch tyvek gs and use GG Polycro, get Titanium needle stakes
2) GG Polycro Groundsheet (2 oz.) mine lasted me the entire 2,200 miles without a single tear.
3) Vargo, or Mountain Fitter, or similar Titanium Hook Stakes. Light and super strong.
1) Stick with the Ti-Tri Sidewinder. Haven't used it myself but hear very good things about it. Should be fine with that.
2) Evernew Pot
3) 8 oz. Soda Bottle for Fuel
4) McDonalds 8 oz. Coffee Mug (don't bring the Titanium mug...I wouldn't at least)
5) Titanium Spork (won't break like the annoying Light My Fire plastic ones...and won't break while eating Ice Cream :-D )
1) Aqua Mira is probably the most popular option. I used a Steripen for myself and loved it. Not sure if that would be economical for two people.
2) I'd bring 2 1L Gatorade water bottles. Free after you get a nice beverage out of them. And easily replaced. I found that collapsable containers started to leak on me after a week or two and stopped using them.
1) I brought a Gizmo on my trip and it worked fine. Just not the brightest for night hiking. I kind of wish I had a red light feature on mine sometimes.
2) Bring a Photon Micro as emergency backup.
1) I carried Black Diamond Trail Ergo Cork and they still work even after over 3,000 miles of trails. Keep the BD's.
Socks: I had NOT A SINGLE BLISTER IN 2,200 MILES WITH INJINJI TOE SOCKS. Just saying its worth trying one pair and seeing what you think.
1) I have wide big feet and used Salomon XA Pro 3D Ultra 2 Trail Runners ($125 / pair) and used 3 1/2 pairs on the whole trail with Superfeet or SOLE Dean Karnazes Signature Insoles in them and they worked awesome. Just a thought.
1) for winter I'd keep the REI stuff, but buy some DriDucks ($15 for a pair at "The Sports Authority" online) for summer as they will actually breath WAY better and be lighter than your REI stuff. I didn't even carry pants, just the jacket for summer.
1) Exofficio is pretty good stuff. I hiked in running shirts and running shorts the whole trail, expect for NJ and then I hiked in my Rail Riders Eco-Mesh LS Top and Pants.
Tired and should be in bed by now. Try putting all your items into a word document and use GearGrams (found online, just google it, make your gear list, and then link it to your BPL posting so people can see weights of what your considering).
BUY A CHEAP SCALE AT WALMART. that will go grams / oz. etc. Mine goes up to 5 lbs and I think I paid $12. It will be the most import thing you purchase for your hike.