Science Gaps in Firefly

Over the last few weeks we have been catching up on Firefly and Serenity, the Joss Whedon "Sci-fi" series. Why the quotes? It's fine entertainment, good story telling, but on the second time through the movie, there are a few points that bother me more now than they did the first time around. Yes, they do the "no sound in space" thing right, but:

1. This is really a "space western". It is a western seasoned with some sci-fi elements.
2. The distance between planets is, literally, astronomical. How do they get from planet to planet so quickly? Not even mention of a device to traverse those distances.
3. There is a scene where a region of space is described as "Reavers' Space". Are you going to tell me that there are enough Reavers to populate the whole space around a planet? That's a lot of cannibalistic psychotics to feed.
4. And while we are on the topic of Reavers, operating space ships and running raids together sounds a bit beyond perpetually berserk killers. What keeps them from attacking each other?