I havent worked with coding myself, but I have attempted to code with several languages and I struggled, ofcourse the devs know the coding language so they are proficient. I'm fully aware of that he did this on his sparetime. I want to emphasize on amount of time it takes for 1 person to implement the storage and inventory update.
I totally agree with you here when quoting Macdaddy above.This is just wishful thinking,but in reality I dont think anything else will happen in gw1 anymore.
If you need help with coding or anything IT related feel free to drop me a dm.
I'd say there are some great tutorials over the internet but if you're just attempting without having the basic knowledge you won't go far without struggling. As a starter you should read about the basic of loops if you're working with anything other than python, vectorization if you work with python. Also read about time complexity since it's better to start with the good programming basis. If you don't understand anything about time complexity, just leave it aside but it will come handy if you want to build an app on your own at some point !
And perhaps begin with an easy to learn language such as JAVA or Python. Leave C,C#,C++, php aside.