Honestly if you want to play around with a local graphing note taker which stores stuff neatly in plain text then you may just want to look into trying Obsidian (https://obsidian.md/)
Honestly that looks like it does 90% of whats wanted and appears pretty user friendly (way more than fucking around with elisp), it's got cross-platform support (Windows, Mac, Linux). Only thing missing is a mobile app.
Mastodon is a federated microblogging network, so with an account on any instance you can communicate with people on other instances. This one is for friendly people part of, or associated with, the geeky/roleplayer social group of Hanging Town (Lancaster) in the UK.