1. A VPN doesn't protect you at all against bad content you download from a file sharing site. You get exactly the same bytes on your PC when you download from a sharing site via your ISP only or via your ISP combined with a VPN network. It only takes longer because more servers are involved. Our advice: (1) only download from sites you trust, and (2) you can't trust a file sharing site.
2. Ask Suddenlink how to unprotect their modem. Or find another ISP if they don't tell. Why do you want to open ports they consider dangerous?
3. I don't see any objection to using Microsoft cipher-program for wiping free space, but I note it's a function in ccleaner also. Your choice.
4. For protecting against unauthorised reading use Bitlocker that comes with Windows 10 Pro.