Yes, `set foldmethod=indent`

> - Open sub-list in new window

This is something I'm not sure exists as a ready-made solution, you'll have to write a function for that. It's trivial for the majority of cases though.

> - Mark a "task" as done

> - Basic text formatting (italics/strikethrough/monospace)

I use vimwiki that has this, there are a lot of other ways to achieve the same.

> - Easy way to "search everything, show a list of results, jump to the context of the chosen result"

fzf.vim. The above and also supports fuzzy search.