A quality JS developer (Angular, Bootstrap, React, JQuery, Node.JS, etc) with a few years of experience can easily make $100K+ around me.
What machine you use doesn't matter... just get a good monitor and keyboard. MBA neither has a large monitor nor a great keyboard.
It's web development... what OS your machine runs doesn't matter that much.
To answer most of your questions: (1) a fridge cannot cool a PC (2) 64-bit OS for over 3.4GB (3) If a PCIe card fits, it should work (4) Resolution, not screen size (5) Report, not respond to Spam (6) Single-Rail/Non-Modular PSUs are not always better than Multi-Rail/Modular (7) Sequential does not matter as much as random for OS drives (8) Requirements come before hardware for servers