Higurashi No Naku Koro Ni Questions?

Ok so I just finished the first series of Higurashi No Naku Koro Ni (where Rena tries to kill everybody), and there are still a lot of things I don't understand. In the first few episodes, Keiichi kills Rena and Mion because they were trying to kill Keiichi, but did he get injected with the drug or not? And if he did, is that why he clawed his throat open? Because I thought people were clawing their throats open because of the maggots, like what Rena had. But how did Rena get those maggots? Or was it just an illusion? Haha I don't know. And another thing, was it Mion's family that was behind the whole Shrine god thing? And were all the different events told from the different characters all events that actually happened in the story? I thought it was Rika that kept making the month repeating over and over again but then Keiichi remembered what he did to Rena and Mion. I'm sorry for the long list of questions, I'm 12 so I'm a little young to be watching this anime but I found it fascinating. Which character's story did you find most interesting? Thanks for answering!