Avoid to load code by cdn, much better local code

Better jQuery than plain javascript code, more easy to read and less error prone

Keep it simple, better 5 "if" than 1 hanging recursive function

You need to discriminate on the given screen size at load and resize time, that's mostly the reoccuring scheme

You got it, you can change css element properties by javascript code

getBoundingClientRect() is your friend expecially against rapid property value changes

Undoubtly you reached a bottleneck that you can solve mixing js with php code only, that is allowed too

You can also do awesome stuff on dragndrop and Prototype, please try

Avoid other javascript frameworks if they don't make it simpler to you