As another commenter suggested, you should probably use Linux Mint for that purpose, since Mint is far easier to use, plus Tails resets itself upon shutdown so you'd need an external drive for permanent storage.
If you absolutely must stay on Windows, there's a project called Atlas OS that tries to strip a Windows installation of its telemetry and bloat, however there are privacy concerns with that, like up until a little while ago it actually disabled Windows Defender by default
I've had good experiences at thrift stores, especially local ones. While they're definitely filled with basic stuff like t-shirts, I've found plenty of cool stuff too. They're not one-stop shops for sure though, you'd wanna do a few stops at a couple to get a really diverse wardrobe. I'm also the kind of person to wander and look at other stuff in thrift stores too, I've found some cool historical stuff about my area in them.
As far as the organizations behind them go, I'd generally try to avoid chains like Goodwill or Salvation Army because they've done (and probably are still doing) some sucky stuff, if I remember right Salvation Army donates/d to anti-LGBT groups and Goodwill exploits disabled people, but I have no sources on hand so take it as you will.