snowshoes are now required in the high peaks, on your feet. So people shouldn't be postholing anymore, and you shouldn't plan to carry your snowshoes at all for the most part (although you may be able to switch to crampons, but check the high peaks regulations).
I am too cheap and maybe too poor to buy all the gear I want, so I get by with what I have. If you really have an unlimited budget and need to buy everything, you do have some great choices these days. I really like softshells for deep winter (the midweight to heavyweight versions: wb400 or dryskin or powershield), since they are much more breathable while still providing snow protection, and rain is not much of risk. But, if buying new, getting eVent hard shells would also be very attractive.
Generally, I think you can skip a windshirt in the winter, since you are bringing a hardshell and probably wearing it most of the time. I do think about getting a hooded windshirt and using that over the softshell instead, but I don't know if I would skip a hardshell on a summit day type of hike. Any shell used in the winter needs to be tough and snag resistant. Once you get up over 3000 feet, into the deep snow and the spruce forest, the trail is often a tight, steep tunnel through the tops of trees, and that can involve a lot of dragging yourself through.
Not sure it makes much sense to focus on UL for the clothing you will wear in the winter, at least don't prioritize that over protection and moisture management. Weight makes a huge difference though in what you carry, so paying for UL can be well worth it. I would love the BPL cocoon pullover for example. But UL makes a lot of sense, and a huge difference, in the amount and weight of the survival gear you bring. I struggle with the question of:
bag vs. bivy vs. stove vs. insulation vs. tarp, etc
I don't bring a bag and that is probably pushing it, but my bags don't really fit in my pack and weight too much. I have a hard time thinking about sitting in a hole in the snow with a broken leg without a bivy, so I bring that. I sometimes bring an esbit stove, but I am pretty sure it is not worth it and should test that in my woods this winter in real conditions to see if that really works. I have been thinking about getting a poncho tarp to use as an emergency shelter in the winter, since you could maybe use a stove under that, but don't own one and would probably only bring that on group trips.
Water is the other killer. I carry 100+ oz of water for a day trip, and my days are much shorter than a high peak summit would involve. At some point you may need to just bring a stove to melt snow, but that takes time and you tired and I would not want to stop on the descent to do that. So 5-6 lbs of water most likely as a minimum, and you need to keep that from freezing.
But otherwise, it sounds like fun.