I've climbed both of these mountains in the past year. Before this I was a bit of a novice, so I can understand your concerns. All the websites will give you a very long lengthy list of things to bring (everything but the kitchen sink), and you won't end up really needing most of it.
The trick to staying warm is just to stay dry and to change into dry clothes whenever you get to camp before your body temperature drops. I wish someone had told me this first.
You don't really need a down jacket on Kili and I saw plenty of people do Aconcagua without one as well. Kili in particular is just not that cold. Layering a bunch with a waterproof goretex shell on top will suffice just fine. Spend your money on a good goretex shell. I used the OUTDOOR RESEARCH FORAY jacket and recommend it.
That said
definitely bring some sort of puffy down jacket as you will be more comfortable, especially when just lying around camp. The only time I wore my down on Kili was at camp when I was sitting in the mess tent hanging out. Even on summit night it's not that cold. Barely freezing.
My down jacket was most useful as a pillow.
I'm not familiar with any of the jackets that you mentioned. I would say that you dont need anything fancy. I climbed Kili and Aconcagua with a knockoff northface jacket that I bought in Vietnam for 50 dollars. I think you could buy something at WALMART, or the equivalent, for around 30-50 bucks and probably have plenty of jacket for both of these mountains truth be told.
Once again, the trick is just to stay dry and to change into dry clothes whenever you get to camp before your body temperature drops. If you don't you will suddenly find yourself very cold and having a -30 sleeping bag and 500 dollar down jacket won't actually help much unless you get rid of that layer. In fact, your probably better stripping completely naked and getting in your sleeping bag if you don't have dry base layers. It's a bit counterintuitive, but it's the truth.
I climbed Kili in shorts on 3 out of 5 days. On summit night I wore long underware and the goretex shell (top and bottom) with cheap wool gloves (the kind you buy at a petrol/gas station). We all started with warm down jackets and took them off within 30 minutes of starting our climb. I ended up not even wearing my gloves for most of it.
I was never cold at any point on either mountain provided that I was 1) dry and 2) moving. The only parts of me that got cold were usually my feet (when my socks were wet) or my upperbody if I neglected to change into something dry (having gotten sweaty) when I stopped moving at the end of the day. If you don't do that you'll be surprised how cold youll get and how quickly. Putting on that down jacket isn't much use if you don't change that bottom layer. My advice is to make sure you have three base layers of synthetic material that dries easily and that you make sure to dry them each day. I actually prefer just nike synthetic sports shirts for this. Then layer up as needed. Keep a fresh pair of socks for summit day. Don't use them until then.
There will be lots of people on Kili with 10k worth of new shiny gear. But you'll also see the porters climbing it in next to nothing: cheap nylon wind pants, an old wool hat, and a cheap pancho. What YOU will need is somewhere in between that spectrum.
Aconcagua is definitely colder, but the main thing is the wind. When its windy and dark you don't really want to be outside for very long without good boots and and mitts. During the day its usually sunny and in this case you won't be that cold. The good news is that, unless you are ungodly slow, there is no reason to be outside on Aconcagua at night, I started my summit day at 9:30 A.M. and was back at camp by 4 pm. Just make sure you have something to cover all your skin in your pack to protect you from frost bite (caused by the wind). A scarf or buff is perfect, it doesn't need to be thick or heavy. That's usually good enough.
Your experience on Kili will greatly inform your needs for Aconcagua, everybody handles cold a little differently. However, don't feel like you need to buy a 500 dollar jacket. If you can afford it great.
I found handwarmers and toe warmers useless on aconcagua. They didn't even seem to work. I threw them away. I did, however, resort to putting my socks in my cooking pot to try and get any moisture out of them at 6000 meters on Aconcagua.
So keep some dry socks. Here are links to my videos for Kili and Aconcagua. I'll warn you, they are quite long (and probably a bit boring and egotistical), so you might want to just skip to the parts that you need. (I made them for my family and myself) But they will give you a great idea of the weather and what you need to wear and when.
Kili
https://vimeo.com/gregpechorin/tylerkiliAconcagua
Kili was an absolute joy. You're gonna love it.