It's usually arranged very similar to a hip hop beat but with a bridge for the 3rd verse and sometimes pre choruses before the hooks. R&B also seems to start with the verse more often then hip hop, but majority still goes right into the hook at the start. If your tempo is slow around 60-70bpm then use 8 bar or 12 bar verses, if it's mid tempo 80-100 then use 16 bar verses.