You raise 20 questions; here is just the first thought.
Many times I need to work locally to debug, as you point out, but don't forget about the <base> tag.
Put <base href=original-url> at the start of the file and then you don't have to have localized every css every js etc.
Just the one you're modifying or unminimizing.

We have jdb and many other debugging facilities built into edbrowse,
and I have no problem with that as long as the user doesn't accidentally stumble upon them.
More flags, more options to do more things, I have no problem with that.
You have done more in this area than I, so think of how we might activate some of these automatically based on a flag or some such.
Deminimizing js as we go is probably the most valuable, maybe a jmin toggle flag or something,
but as you say you have to dip into scripts[n].data, since the original source is mminimized.
Well scripts[n].src tells you wherre the js came from, so probably not hard to put it all together.
I assume your deminimizing code is open source and could be put into startwindow.js with the proper license, as we did with jotform.

Karl Dahlke