Hi Derek,
Just noting that although BS4 alpha 6 has been out since January and the Beta is supposedly due 'soon', Boost itself is still built using Alpha4 (as was available when it Boost was first created). I assume HQ are waiting on a Beta release before updating.
I don't think there are huge differences in code, although the integration of flexbox is a fairly big change in the background, but it is worth just being aware, as there are some changes.
As for editors - I generally use Geany (on Linux) or Notepad++ (on Windows)
But for comparison, have recently been doing some work with WordPress - and found that the editor there (or at least the widgets in the theme being used, so could be the particular WP theme I suppose - its use of bootstrap was 'quirky' to say the least!) is even worse, and less consistent, about stripping html. There, it seems, if you put html in and never visit the visual editor, you can often get away without it being stripped, but the minute you visit the visual editor it strips it. Very frustrating - especially when working with others. You just get something the way you want it in the text editor - and someone else views it in the visual editor and all your html suddenly vanishes! :D