Wow, you are really fast!
I had a quick look and the folding by shortcut now works almost perfectly. The only thing I noticed is that folding all sections with the shortcut Ctrl-K Ctrl-1 does not work reliably in all situations yet. For example, if you have only one depth of headings in a document (# Heading 1, # Heading 2, # Heading 3), the first section is generally not folded. However, if you have multiple depths in the headings (# Heading 1 ##, Heading 1.1, ### Heading 1.1.1) it works perfectly! The next one is maybe a habit from org-mode, but don't you think that the shortcut to fold the current selection, should unfold the selection too? ;)
By the way: it is not self-evident how fast you fix the bugs and add new features here. It's very motivating for me personally to see your working zeal. You are doing a damn great job :)