[megakwood]

There is a great app called Hyperdock that does exactly what you want with window snapping. It works so perfectly that I sometimes forget that it's not a native feature of OS X.

Not sure about your window size problems with external monitors, I find that OS X handles this amazingly well

[Prefinem]

I forgot I had Hyperdock on my last Mac and when I got my new one I thought it was broken because it wouldn't snap / scoll maximize.

It has probably been my favorite utility for Mac