You seem to be aware of many things.

Just for communication you are using more unfree tools then free and more then in the other categories.

A question with no right answer, because it is a matter of taste and habits.

Both are very much sophisticated desktop environments which very useful defaults. Neither Gnome nor Plasma are too complicated for beginners and can be customized easily. If you want to you can go very deep into the customization too.

If you just want to save the text to read later, go with HTML.

If you want to archive it with graphical elements and embedded images, PDF is the better choice.

What I find kind of strange is that they have used Gmail before. Feels not to be the best decision for a VPN service which offers anonymous access.

Even better that they have switched now.

A combination of different.

For brainstorming Logseq is great, for tasks I use CalDAV in combination with Thunderbird and JTX Board (Android) a lot.

Briar has that.

Could also be a brain though.

Reminds me on https://userinyerface.com/