<PERSON> is an amazing writer (except for his inability to finish stories). However, he very much likes to write in a way where the reader is thrown into a universe without knowing the mechanics and the history and has to figure things as they go. This can either be ok or really annoying. I actually like it, though he has, in practice, put spoilers into the story.
The publication order doesn't match the chronology In addition, thanks to time story threads and relativity, it's hard to determine chronological order. In fact, the moment of transformation is not described in any of the novels (AFAIK). You are left to imagine how fast or when exactly it happened.
I would suggest reading all of the Revelation Space books together. I started with Revalation space, then read Chasm City, then went to the sequel pair. If I remember correctly, the order for what I consider the "main series" is "revelation space", "redemption ark", and "absolution gap". Absolution pretty much ends the story, if I remember correctly. 55
Though he could always continue - <PERSON> pulled this trick very nicely.
Chasm city takes place separately (and is a great book otherwise) and I found it enjoyable after Revelation Space where I already knew what happens to the band. Then I read Diamond Dogs (short story) which relates to Chasm City. There are also related stories in Galactic North.
The Prefect takes place in the glitter band earlier, and just mentions something bad happening in the future (the conjoiners appear in that book as well). I read it later.
<PERSON>' other books are each standalone in a different universie - Century Rain is about alternate worlds, Pushing Ice is close-to-modern-day and seems like a <PERSON> tribute. House of suns is weaker and plays with extremely long periods of time (galaxy spanning). Terminal World talks about an earth in the future with "Zones" (a-la <PERSON>).
As for your second question - The Melding Plague is the name of the transformation. The Rust belt is what happens to the glitter band after the plague. You won't get a good idea of what happened - Just of life before and after. <PERSON> makes these places seem "alive". 322