Weave qeustion......................…

I'm 13, I have kinky, puffy hair. I straighten it. I wanna get a weave, but I have dandruff and I wash my hair every week. How can I get a weave? Is there any way to get rid of dandruff temporarily without washing your hair? How long can you keep a (sew-in) weave in? How much does it cost to touch up a relaxer? How often do you have to touch up a relaxer? Are relaxers really really harmful to your hair?