I use notepad. Pretty sure there are numerous editors out there that would support lua, but so far as long as I type correctly notepad is fine
I have had a long background of coding since the ZX Spectrum which got me started. Mostly I have used variants of BASIC as that was the language I used on the Speccy. obviously things change over the years, but the concepts are pretty much the same as when I programmed on the Spectrum, just with more commands and a smidge more memory
I have used numerous packages since on the Amiga and PC and so picking up Lua has been fairly easy in the main so far. I have learned mostly from examples and studying the commands available, also browsed the main lua online docs a little, but not much in actuality. Most I have learned from digging in and trying things. Admittedly having a background knowledge of coding helps, and there's only one way to do that. Read, and practice a lot. I can only say that I have many years of coding under my belt, so it is hard to remember back to the days when I knew nothing. but when I started I read as much as I could (not so easy back then, no internet) and wrote and rewrote many programs until I could do it without having to think too hard.
Things are much easier now, with many languages available with more features and commands than the Speccy could dream of, or even fit in memory
48k was not a lot, and you didn't actually get 48k all to yourself. Lol, text files are bigger these days.
Check out the scripts included with reloaded, check out general programming principles. Nothing stopping you from at least doing some simple scripts to start, and work up to more advanced stuff.
SPECS: Q6600 CPU. Nvidia 660GTX. 8 Gig Memory. Win 7.