Yes I am using sublime text 3 for all scripting. The plan is to eventually add similar functions as Sublime Text & Github's Atom text editor such as auto-complete, multi-line / multi-word editing, search & replace etc & hopefully a dark & light theme option.
For now though I recommend using Sublime Text, Atom or even Notepad++ for writing your scripts in.
Here's a quick tip for you: You can actually include external lua files in Visionaire Studio with a small function, which means you don't actually even after use the built in script / text editor once you add some include scripts / functions to your project... however I do recommend directly pasting in the final version of your scripts to VS as opposed to having them as external files, as they should load faster internally, plus they are more secure from tampering when internally included.
Please check this
wiki page, for more information on how to include external lua script files. Technically it should even be easy enough to update the script to contain a table & for table to iterate through the table, so you don't have to write unique functions for each external file.