To answer the stove question, I find the single most important factor is how warm the fuel canister is. If you don’t keep it warm, the fuel will trickle out, and you will use MORE fuel to melt snow or boil water.
Keep in mind that as the fuel exits the canister, it is going to lose heat on its own. Even in a warm place, it will get colder. This means if you use a neoprene or cloth insulator on its own, the canister is going to just get colder.
Your answer then is to actually apply heat to the canister.
There are several decent methods:
1. Simplest: grab the canister with your bare hands. It isn’t fun, but it works.
2. Use gloves(ideally ones that you do not care about) and alternate between grabbing the hot pot of water(which heats the gloves) and then grab the canister. This is more effective, but you will likely damage the gloves you use. Ice climbing gloves aren’t typically cheap…
3. Once you have some snow melted, pick up the cold canister and dunk it in the water. This works amazingly well, but you find yourself juggling fuel canisters. I like to use nearly-empty fuel canisters to keep the pot of water warm while I dunk a full canister in the pot.
4. Construct a device that channels the warmth of the pot around the canister. This could be a series of wires that create a harness around the canister. This is hard to make, because the wires easily burn whatever container they sit in. I haven’t seen a good system yet.
5. Keep the canisters pre-heated in your jacket or sleeping bag before you use them. If you just do this and then keep it warm using strategies 1-3, you’ll probably get by.
Something to be careful with:
You can use a plastic container, fill it with water, and submerge the canister into the water puddle. At a cold bivy in Alaska, the canister got so cold that the puddle of water froze to the canister, and we had to carry around a piece of ice or throw chip it away, and then it was still attached to the plastic. If you are going to use this method, make sure to use a larger amount of water, ideally hot water.
Also, I find jetboil stoves are less and less useful the higher you go. I have bivied with the MSR Reactor with no problem at 20,000ft, and seen jetboils fail over and over again at altitude. If you are not using a tent, the Windburner might work better.
Finally, make sure to test out your new system on a normal day of winter climbing before taking it somewhere huge.
I’ll let someone else answer the food question!