This scale-key-chord thing is mind boggling. I wonder what is the right method to learning music theory?
Shall we learn about the chords first and then scales or the other way round?
To the extent that these subtopics are very interrelated, it doesn't really matter which one you start with. Whichever appeals to you is probably the best, all else being equal. Chords are of course built out of scales, so you could learn some chords first, then something about scales, then analyze the scales that are used to build those basic chords. At some point, if you're doing it right, they pretty much cease to be separate areas, and just become part of your harmonic analysis arsenal. Any scale can be harmonized into a spectrum of chords.