ISTR that someone had done an IntelliJ plug-in for lua, but that seems to me like overkill for developing in an environment that's mostly specialized API. (I think the person who did it used IntelliJ professionally and didn't want to switch.) Most of Clown's suggestions above do syntax highlighting and paren matching, though not function or variable name auto-complete. And since Clown mentioned vim, I feel obligated to add EMACS to the list.
As for version control repos, I think the preference is left up to the add-on developer(s). And again, it's probably overkill to use either for little, one-person projects, which most of ESOUI's offerings are (with some exceptions).
tl;dr: You're probably attributing more sophistication to add-on development than it usually has!