I listened and analyzed hundreds and hundreds of instrumentals (seriously) just to learn what you're seeking to learn now. Honestly, 95% (a lil'exagerated) of Urban music, (Hip Hop, R&B, Dance, Crunk) Stick to a small number of chord progressions. Mind you, there don't need to be 3 keys touched simotaneusly to be a chord. A chord progression only points to what are you based in for that measure.
Yeah by Lil' John or Babyboy (beyonce) by Scott Storch contain no exact "chords" as one might think of them, but there are chord progressions present. Both the same at that. The single most common chord progression is Urban music is 1m - 4m(or 6M). Am to Dm(FM), Eb to Ab (or B). Or the one special occasion of 6 to 1 which was in Dr. Dre's Higher for The Game. For those that want to check my logic, download the instrumental and play along with it. It goes from B to Eb. But without the thirds in the chord. I can name unlimited songs that go from I to IV (or VI) I keep saying or because the 4 chord and the 6 are interchangeable, pending on the bass. This chordprogression alone can lead you to making hip hop and rnb.
There are many more things but I'll leave you with that. But one more thing, for the sound hunters out there, a scale that I've found to be named in music theory, but I've never seen used in any other genre but hip hop is Phrygian. Learn the Phrygian scale and you'll have a trick up your sleeve.