As a note, for #4:
4. fresh reboot + running strive + looking at portrait folder in game
That's basically expected behavior with base game, it loads every single portrait into memory, and it's loading their uncompressed raw format which is significantly larger than their on-disk size.Now that I re-read the other numbers, it actually seems your memory usage is basically in-line with my own. At least I assume #2 is an add-on to #1, and thus it's using around 300-400mb. Not sure why you're looking at system wide values though, much simpler to just look at Strive.exe. Working set numbers are the more useful ones, they show up in Physical Memory if you do properties on Strive.exe in process explorer.
If you want to reduce memory for loading of the portraits folder, that's why I added the delayed loading mod.