My goal is to be able to accompany a song with chords by ear on my ukulele.
Now, irrespective of keys:
Should I try to learn all of the diatonic chords of each key, or just certain important ones? (I, IV, V, V7 and maybe vii°?)
Are there any weird chords (mostly four note chords) that I should learn? Are there some four note chords that are more important than certain diatonic chords and should be learned first? (Obviously, things like dominant 7ths are important, but what else would be a good tool?)
As far as keys go, are some keys more common than others? (Obviously C, G, D, A are common, but are there others that I should learn sooner than later as well?)
Ear training is of course an important part of this equation as well, but that's for another question! This is about how I should strategize learning chords, which chords I should learn, and how I should practice them. Obviously there are a lot of parts to this question, but don't feel like you have to address all of them. The over-arching theme is what chords should I target learning so I'll be able to play the most music sooner?