1a - NTFS. Some may recommend exFAT but I strongly don’t recommend it, it’s not a journaling FS (so may corrup on power loss etc) and awfully slow. I’m pretty sure there’s no problem with NTFS on Linux now, but I don’t guarantee though… I still use the old ntfs-3g fuse driver because I’m lazy to run the latest kernel. It’s slower than the kernel driver, but works well and stable.

1b - Program’s specific feature may not work, malfunction or crash. It surely can corrupt a file e.g. you run a document editor in WINE and the program crashes while the file is open. But usually it tends to work pretty well for many programs these days.

1c - Yes. Go to about:profiles on your Firefox, click “Open folder” and copy your profile folder to your linux install on ~/.mozilla/firefox/

1d - Not that I’m aware of.

1e - Don’t format your existing drive, should be safe then. If you’re really paranoid about losing data, disconnect the drives physically before testing the live distro. Yes the changes not being saved means changes you make to the linux session wouldn’t persist and get reset the next time you boot that live usb. You can access your NTFS drives like normal even on live, there should be no difference to a full install to internal drive.

1f - Unlike Windows where you get programs from each program dev’s website, on Linux you usually install them from your linux distro’s repo. So unless you run sketchy binaries and scripts from 3rd party, it should be safe. You very likely would never get infected by simply browsing. No need to worry about that part. The Linux drive also wouldn’t be accessible to Windows side, so unless your whole system including the Windows drive gets “infected” you’re safe. If that happens you have bigger issues.

1g - Recent-ish nvidia card shouldn’t be an issue. The easiest way to find out is to just trying to boot a live USB and see if things work.

2a - Win10 has multiple versions, like 1609/1703/1709/1803/…/21H2. LTSC is their “long term service channel” where they maintain a specific version for an extended time. They also have multiple editions, Home/Pro/Enterprise etc. What you’re looking for is “Windows 10 Enterprise IoT LTSC 21H2”. IoT means it’s getting 10 years of support unlike normal LTSC which only has 5 years, 21H2 is the latest version. Enterprise (IoT) LTSC is also cleaner (less bloat) than Enterprise.

2b - You can everything you do on the normal editions. It’s hard to legally obtain an Enterprise IoT LTSC license, but it’s no issue since this is your personal machine. (use massgrave ohook or hwid for activation) Unlike normal versions you won’t get pre-installed Candy Crush or Tiktok.

2c - Their method of keeping files should work fine, but it could go wrong. You should backup your existing Windows install if you decide to do this. Use dd on linux, CloneZilla maybe if you favor GUIs, to backup your whole Windows drive as an image you can restore to later. If you do a clean install with LTSC your system would be a bit more cleaner, since “upgrading” from normal Windows does keep the clutter from the normal version. I’d recommend clean install if you don’t tend to spend a lot of time configuring your system. massgrave MAS works fine, no need to buy sketchy keys.

3 - Yes there are those kinda malwares. Theoretically yes, not connecting to the internet at all is the safest. Realistically, if you keep a firewall(your home router in most caes) and block incoming ports, you should be safe. There are people still running WinXP for fun and they don’t get random malwares out of nowhere. Just don’t download anything weird. But anyway, I don’t recommend regular Win10, just switch to IoT LTSC :)

Hope this helps.