I can't answer as to how B5 compares to DS9 because I only lasted about 1.5 seasons of DS9 when I realized I just didn't care about any of the characters and dropped it. At some point I'd like to try it again.
IMO, the characters and plots are very coherent. Some complain that there's a lot of rehashing in the dialogue and that can be true at times. But JMS had chosen to do everything he could to ensure that a person could tune in to any episode and not be lost and there are only a handful of 'Previously on...' clips done throughout the series.
Nobody there is exactly what he appears. I envy the folks who get to see it the first two times. Yes, two. Because the second time you'll really appreciate all the things that were set up *long* in advance.