Apple iPhone 5 (Americas GSM)

I'm very picky about my phones. As I've read on here there seems to be no problem about switcing from an Android to an Iphone, so I'm not too concerned. The only thing that has me second guessing myself is my music. I have a little music on my android that is on my SD card, so will that switch over? And also, Itunes. It's always confused me. You have to pay for every song? And I've always heard that if you just plug your phone into someones computer that has Itunes and you have an Iphone that their music can get on your phone and it can delete your music or something like that. And ive also heard about it getting virus' or something...
My mom, back in the day, had an Ipod player that was just the small box that clipped on and she plugged it in one day to download music and it deleted everything on there without her knowing. So that's just always confused me, but then again she is kind of clueless about stuff like this so she could have done it herself?

I just need help :\ Christmas is coming fast!!!