If you are focussing mostly on the front end, include Theme Components in your reading.
I would also recommend you took most notice of plugins or TCs that use:
- native Ember over jQuery/brute force DOM manipulation
- the Widget system
- vanilla javascript over jQuery (where direct Dom manipulation is absolutely necessary)
- modern javascript syntax (es6+)
BUT
Rather than bore yourself to pieces reading too much of other peoples code just for the sake of it, can I suggest the most important thing is having an idea you want to implement then look for good examples of how to do that from similar existing instances? You will be more motivated if you have a particular goal you are passionate to achieve and will be more ready to break down any walls you come across (there will be some!). It’s also more fun that way!