I wouldn't reuse plastic bottles - they can wear down over time - especially if they are being steamed/boiled or heated in the dishwasher. You're supposed to get rid of plastic bottles when the plastic becomes cloudy, scratched, etc. If they're glass its fine, I would reuse them and just get new nipples.
On the brands, I tried Dr. Brown's but DS seemed to prefer the Borne Free and Playtex bottles. Each of those brands had fewer parts to deal with and the Dr. Brown's also leaked on me a few times.
As some of the other posters mentioned, I would return the bulk set and buy smaller sets of varying brands to see what you like (to clean) and what your baby prefers. Babies will have different preferences and it will be a sham to waste the money on the Doc Browns if your baby doesn't like it.