Hey! I'd love to help you out! It can be a little intimidating at first, but once you've gotten the hang of it you can do pretty much anything with Twine!
My biggest general advice is to figure out what you want to do first, and then work backwards. For example, I didn't know how to accomplish the clothing system, I just decided what I wanted it to be like and figured out how to do it from there. You learn more from needing to do something to accomplish a goal than from reading about how to do something in the abstract.
My two other big pieces of advice are to find and use other people's macros (there's no point reinventing the wheel, if somebody's already made a superior inventory system, go with that!) and use widgets very liberally. The widget macro basically lets you run the same big block of Twine code using just one line, and with a big RPG style thing like this, it really comes in handy. When a scene ends, instead of manually typing in or copy and pasting all of the necessary code, I can just slap in "<<completelead>>" and all of that is done for me. Be thrifty, conserve your time.
If you ever need any specific help, please feel free to send me a message or an ask over on my tumblr!