This is quite awesome! Unfortunately as far as servicing goes the machine has been sitting in our basement for years, no work has been done on it. I'm glad its still working, hopefully I can deal with the capacitors before its too late. It has its original hard drive which still works and has some cool old games on it and its running the original MacOS 9.
Wow I had no clue it would be possible to develop on the machine itself! I'm glad people have maintained archives of this system's software, it may be worth it to develop on the iMac itself, thank you!
The main advantage of CLI is that its easier to instruct people on what to do and easier to get answers from people about how to use a CLI, and you can copy paste. If you know how to use the GUI though it can be a powerful tool as well.
You'll probably want to switch off it one day, but when I first got into Linux I used Ubuntu and everything just worked. Even when I had a laptop with a touchscreen, the touchscreen worked no problem. Its a great place to start imo, but not a great place to stay as when you become more proficient with Linux you'll start to see the distro's limitations.
I want to preserve the MacOS 9 on the iMac, but I think I'll do this on the 2005 Mac Mini.