I use IntelliJ with the mentioned plugin or Notepad++ for quick edits. You get the syntax highlighting, some error checking (without compiling). As well, someone put up autocomplete files for the API awhile back.
SVN or Git is mainly down to preference, especially since most authors develop solo. You do want to have some sort of VCS though, even if solo-developing. It allows you to save and version your work. You can try out new features on a separate branch and easily fall back if it doesn't work out. As well, you can stash your work, go back to the last release to push out a bugfix, then resume your work.
By the way, the Git on ESOUI (
http://git.esoui.com/) is separate from Github. You lose some of the tracking and pull features on Github, but have the package to zip here. Of course, you could easily have Github and Esoui both as remotes.