Welcome to the world of chins! haha. you will find a lotttt of conflicting information about chinchillas. Not many people are too knowledgeable about them and some people that are not will still argue that they are. As for your questions:
I do not give raisins. I used to when i first started out with chins, but most people here would agree they have too much sugar. Usually, the blander the treat the better. The only regular treats I give are non-frosted shredded wheat, cheerios and the occasional oats (old fashioned). All of these have no sugar. Once in a while I give rosehips or rosebuds.
People will argue both sides for which genders get together better in pairs. In the wild, I believe it's large amounts of girls together, but people do have luck with boy pairs. The general rule is, there is no rule with chins in pairs. You never know what you're going to get. Right now, I have a pair of boys, a trio of boys and a single boy. My trio and pair get along great, but thats just for today. Some people don't even bother with introducing chins to each other because it is so unpredictable.
Plastic is NOT recommended here. I'm sure you've realized chins are chewers and they will chew whatever is in their cage, whether its plastic or wood. If the plastic is chewed, it can cause an impaction which means it gets stuck in the intestines... this can lead to many problems. Some chins are not plastic chewers, but it's usually better to just not take the risk. I always use chin-safe wood, the ledges in my cages are kiln-dried pine.
Again, people will argue both sides with this. Both genders have their ups and downs. Girls usually are more likely to spray (pee!) long distances, but i have one boy who does. I just ended up with all boys, but I love them all more than anything. They are all very affectionate, but people who have all girls could argue the same. I hear sometimes that girls are a bit more moody than boys, but isn't that true for humans too? :tease:
Anyway, like I said you'll find different information everywhere. For the most part, I trust the people on here more than anyone else and order my food, hay, toys, etc. from my friends on here. It's been working out in my favor so far
Hope that helps a bit! Good luck!
ETA: Dang, Beck and Susan... you beat me to the punch!