Apologies as I've not read all the replies in this thread, so perhaps duplicate comments.
Overall I quite like your logic and plan. I agree with the idea of using gear you already own insofar as it will do the job, so your swapping sleeping bag plan sounds right to me; I used a WM 20F bag until after the sierras and swapped to the very same (Summerlite) bag after that, and was happy throughout.
Adding a thinlight --- or two --- is a good option. Consider having at least a 1/4" (not 1/8" thinlight) from the start just because there's more stuff in the first 700 miles or so that can pop your neo-air than you'll encounter later. On the CDT this year, I liked two 1/8" thinlights to start the trip, mailed one home when out of the snow, and eventually mailed the other home (when definitely done with snow). So I didn't practice what I just preached here this year in New Mexico and it worked fine for me --- FWIW.
I think the Circuit is a great choice of pack. I personally wouldn't swap to a lighter bag; partly for me now it's just durability. I used Gossamer Gear packs on the PCT and part of the AT, and found they really did get me just about one thru-hike each, whereas my Circuit has now done half the AT and all of the CDT this year and is still going strong, and I've heard similar things from friends. It's a bit heavier, but overall a better and more comfortable pack (for me, at least).
Shaped tarp: for a good chunk of the PCT, my tent was more about bug protection than rain shelter. I just carried a poncho as both rain gear and "adequate" tarp until Kennedy Meadows, and that worked for me, but after that I was glad to have a tent with bug mesh --- a single walled tent will work fine. Not optimal always for WA state, but I live there and have done a fair bit of backpacking with a single walled tent, FWIW.
I used a thermawrap jacket throughout. I had a larger thermawrap vest to layer just in the Sierras but didn't actually use it much. I did, however, not hike in a particularly high snow year (2008 for me). The EX Light is a great jacket, I used it this year, but IMO no need to buy new gear if you already own a thermawrap jacket. Just consider something (not too heavy) to beef it up in the Sierras, mail that home along the way if not needed. FWIW, I find now that I use my thermawrap vest more than I do the jacket --- in colder temps for me it's a great piece of gear to hike in, with some sort of wind shell or wind shirt, whereas I normally can't hike in the thermawrap jacket without getting too hot (depends on conditions of course). So layering those two was for me a good combo. I had a size medium jacket and so bought a size large thermawrap vest, and that layered well.
Camp Corsa is a good choice for an axe. Ditto microspikes, can always mail these home if it's clearly not a bad snow year. I was happy without either axe or traction device in my year, but started with both until I could personally assess conditions.
Stove: there's a reason the majority of thru-hikers use alcohol stoves. You can certainly make it with a cannister --- or you can just eat cold. No single right answer here, but ... all things being equal I'd suggest you make a simple stove (such as the Skurka fancy feast --- google it) and try that out a couple of times at home. It's just nice to have more options for getting fuel along the way.
You've clearly thought a lot about this; Best of luck!