From a theory standpoint, there most common harmonies (and therefor 'chords') are Dyads - two note sonorities.
These are kind of bland though, so I'm sure you won't mind if I skip over them
From there, you have in conceptual design (and they way they're taught) this order:
Traditional 'Simple' Triads
Major Triads (C E G)
Minor Triad (C Eb G)
Diminished Triad (C Eb Gb)
Augmented Triad (C E G#)
After that probably come the 7th chords -
Dominant 7th (most common) (C E G Bb)
Major 7th (C E G B)
Minor 7th (C Eb G Bb)
Diminished 7th (C Eb Gb Bbb) (aka. diminished add 6)
Half Diminished 7th (C Eb Gb Bb) (aka. minor 7 b5)
These can branch off into more complex sonorities called Extended Chords
These are your 9th, 11th, and 13th chords. Generally you can do whatever you want with the 9th, 11th, and 13th (C 13th b9 #11 would result in C E G Bb Db F# A), but there are some limits.
Two that I can think of right now are:
1. Something like C minor #9 which would get you C Eb G Bb D#. The Eb and D# are the same thing, so it doesn't make too much sense to double something with a different name. This one would sound more like C minor 7 with a 3rd on top. But then resolution of the D# would go up to E, where as the C minor 7's Eb would go down to D or something.
2. There are some schools of thought that state your 11 should always be #11. But if it's your music, do whatever you want.
Just make it sound good and make sense to you.
Instead of extended chords you could go into other relatively common sonorities such as the augmented 6th chords. Italian, French, German (and Swiss, for those of you who are crazy like I am). Remember, b6 has to be your lowest pitch to pull these off 'legally'
Italian - 1, #4, b6 (C F# Ab) - goes to either V or I6-4
French - 1, #4, b6, 2 (C F# Ab D) - goes to a V or I6-4
German - 1, #4, b6, b3 (C F# Ab Eb) - Goes to a V only*
Swiss - 1, #4, b6, #2 (C F# Ab D#) - Goes to I6-4*
* - people lump the german and swiss into the same chord called just 'german'. This is fine, but I differentiate. Sorry if I offended anyone here. Personally, spelling counts for me and those chords.
After basic triads, sevenths, extended chords, and augmented 6ths, you could go into added or sussed chords
C6 - C E G A
C4 - C E F G
C2 - C D E G
Gsus6 - C E A (kinda like a minor here... hmm
)
Gsus4 - C F G
Gsus2 - C D G
After that it's all functional chords, so context of the chord progression-
The augmented 6ths do this, in that they must be followed by a particular chord.
Neopolitan (or phrygian II chord) does this. It's a first-inversion (3rd on the bottom) of a Major flatted two chord. So in C major (or minor) it's Db F Ab, with F as your lowest pitch.
Then you could always do secondary dominants - V/vi going to a vi of course. That kind of thing.
Then if you're feeling even more spry, you can go into quartal chords and secundal chords -
Quartal:
Augmented - (doesn't exist... C F# B#) ((B# and C are the same))
Major - C F# B
Minor - C F B
Diminished - C F Bb
Secundal:
Augmented - C D E
Major - C D Eb
Minor - C Db Eb
Diminished - C Db Ebb
Then you can get even crazier here and go into making extended chords and (essentially) 7th chords for the quartal and secundal sonorities.
If you can compute all these different things in your head, you're ready to make rationalizations for nearly any kind of grouping of notes. I've personally made a system to explain any set of pitches (from the 12 tone scale) you can come up with
But that's just me.
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You said
C add9 (only thing I know to call it. It's a C add9 minus the D note)x3
C add 9 is like... C E G D.... (also called C2). I think you meant to say "minus the B note". If you mean your chord is C E G D, then yes; add9 is fine.
And the only thing that's unusual here is that you're going from A to Bb to B. It's just a chromatic passing chord. it's not too strange, and will sound like you're putting a bridge linking the B minor the the A minor.
Cheers!