What I had to do to get started again was just jump in. A couple handy tips though.
* Use VSCode to edit the files, it's a very powerful cross platform editor made by Microsoft with a lot of well made extensions available. Can open your entire UI folder and have all the files present on the explorer tab. Can also open multiple folders, for example I keep my UI's folder and the default folder open in the workspace associated with my UI.
* Keep SIDL.xml open as a reference. This is really the only actual documentation we have to what things exist in the UI system. As far as how to use each of the things, pretty much have to go on a hunt through the default UI to find examples. The old AboutSIDL.doc never got any updates so that's only really helpful for the most rudimentary of functionality.
"Computers are like Air Conditioners, they stop working properly when you open Windows."