Alright, so I decided to do the crazy thing and make my own 20 degree down top and underquilt. My friends found out and now I'm apparently making 3 sets of them (plus one synthetic). I'm a masochist, it would seem. I have done quite a lot of research and think 800-850 fp is going to be my best bet, but I'm left with two major questions:

1. Is DWR/HyperDry/treated down necessary?

2. Where the heck can I get roughly 100 oz of 800-850 fp down without breaking the bank? I've messaged a few places that people mentioned here and on the ultralight backpacking site (some of the info is out of date), but haven't heard back from anyone. RipStop By the Roll was the best price I could find, but who do y'all prefer? Does anyone give discounts on big quantities?

Ok, those are my most important questions for now. I'm sure I'll have more. Thank you all in advance for your help! I should also apologize if I didn't dig deep enough in the threads... I'm still figuring out how to use this site.

Also, shoutout to the wonderful madman who created the CatSplat UQ Calculator. What an invaluable resource!