Such a nice thread when people are committed to helping others!
Thanks a lot @phl for the expertise and the time to look through those guides and write all the details of the best practices. And thanks @whoami for bringing up the question and following though with those nice guiding pictures.
I think this effort deserves to be consolidated into a guide! (Perhaps on the unofficial docs). I’ll try to find the time to compile this over the next weeks. But I’ll have to do some reading on ssh-agents first 
@phl Is it ok if I grab some explanations from your posts too onto that?