Get the latest White Dwarf for Renegades and the new and improved Red Corsairs, called the Astral Claws back when they used to serve the Emperor. If you havent done that already you will be pleased to know that you think like GW as your ideas are very close to the articles topics. Personally I think its a shame that the Red Corsairs have been given a specific history now, as they used to be Renegades from many different Chapters banded together still wearing their old loyalist power armour with a few chaos stars and glyphs daubed on.
I always thought it was kind of cool to think of individual marines losing their faith and taking off on their own, rather then entire chapters. So you'd get ex space wolves and ex ultramarines etc banding together to form warbands....I used the word "band" a lot in that post.