Great writeup Maciej. I do have some questions:

(1) Is there an easier secure way to open attachments to Emails? This is a critical point of error in campaigns, and yet your suggested solutions are lacking in my eyes. I for one do not use a smart phone, and even when I use a Gmail account I use the html version that does not have a Google Docs option for files. So I am left with your option 3, and this could take several minutes in contrast to double clicking the file.

(2) Why do you recommend to avoid SMS but to treat Twitter/Slack as a public messaging option? Why not just treat all three as public?

(3) Why do you recommend only Chrome browser? In particular, why not Firefox or Tor?