1. I mean, there's iSH to emulate an x86 linux environment, but it's not like you can get access to the iOS system through a terminal. Since I mainly use the terminal on my phone for SSH, I use Termius.

2. There's the official wireguard client

3. iOS has native mp4 support. You can play mp4s from files stored on the phone, or from gdrive or dropbox, etc. or just import to your photos/videos library.

4. Yes.

5. yes, the Möbius Sync app