If it's a nice day, it will probably be crowded. Not atrocious like 3 hour lines, but maybe an hour+.
Scream Machine and Rolling Thunder are pretty brutal. KK can also get a pretty good rattle, especially in the back of the train. Some people don't seem to notice this though.
Probably not, though El Toro and Nitro's lines move really fast (unless ET is running one train). If the weather is crappy though, the crowds will be much lighter. Everything usually runs in the rain except KK, as long as there's no thunder/lightning. If it wasn't terribly crowded and you were theree all day you could probably do it, it depends.
Personally I'm not a fan of any of it, but a lot of people like Best of the West which is over the bridge behind the log flume. It's all expensive.
Get there early enough to be at the "rope drop". Superman gets a really long line pretty quickly. Bizarro/Medusa will also get a long line now. Lines also get very short towards closing as people start leaving.