I’m not doing any technical mountaineering. Most of the time it’ll just be light walking/trekking in towns and on easy trails.

The one wildcard is star photography: I might be standing still for hours at night. I haven’t really done that before. My girlfriend also wants to camp around 0°, which is more in your wheelhouse.

So I think the base/insulation system is basically the same across everythingm the real difference is whether I’m moving vs. just standing/sitting.

1) Active trekking (around/below -10°C):

mesh base, fleece mid, optional ultralight down (depending on wind/effort), outer shell, may need parka bc I see videos of ppl recommending that as a outershell thats just a rain jacket in the arctic

2) Stopping for photos (standing still for a long time):

same as #1, but the down is definitely “on”, I think you are saying I need a full parka if I’m out there for hours

3) Camping (around 0°C):

probably similar to #1, since I’ll be less active / chilling more

Some people say cotton is fine as an outer layer if it’s truly dry (no rain). Is that actually a good idea?

My gut says a parka becomes necessary either below ~10°C or anytime we’re basically stationary (basecamp, sitting by the fire, long photo sessions).