I just said to my parents that I'm dressing up for a con cos it's the norm :P I get most of my stuff from charity shops and amazon/ebay, cheap stuff with decent reviews. If you can alter what you find in charity shops the better, doesn't have to be exact. Anything else, internet! If you have some friends who'd like to go invite them, make a cosplay group or post on con forums and find other homestucks to meet up with, they'll let you in their group and take you with them As for getting ready, sometimes its a thing you have to do alone :P
1. Just tell them like you're going to a concert. No big deal. 2. My friends get their materials from craft stores like Hobby Lobby. What you need depends on what you're cosplaying as. Most common material is fabric and styrofoam. 3. I suggest talking to your own friends about it. Don't ever meet people from Internet. I'm sure at least few of your friends are interested in cosplay also.