What is the most that can be done to secure pseudonymous sign-in's?

Situation: Ones activities require them to create multiple accounts with the same non .onion website, each account requiring a verified email address. Their activities are legal, but they are concerned about a future in which that is no longer the case.

Goal: One desires utmost privacy, and the closest semblance possible to anonymity. Particularly so from a suppositional future attempt to correlate, de-anonymize, and identify the user using backward facing data.

Current Practice: Utilizing a securely set-up Proton suite including mail, vpn, SimpleLogin to create and manage accounts. Running Librewolf with DuckDuckGo, browser is leaking ~17.5 bits of identifying information per Cover Your Tracks - I have no bearing on the scale of that number.

Question: I’m would like to learn the extent to which my goal could be realized, and whether by building a small PC, learning to use Linux (Desbian), and using that as a dedicated host for Whonix I could materially improve conditions.

Cheers, thanks.