Since you enabled AutoEventWireup be sure to comment out the code in OnInit that is wiring up the page load event because that would make it fire the event twice.
Regarding the postback error at /, that is a known issue with the VS Web Server, it doesn't happen in IIS, so if you can use IIS or probably IIS Express instead of VS web server that will solve it for you.
Or move your custom feature to a different page than home page for development purposes and just know that this is a known issue and it doesn't happen in production. It also doesn't happen if using an url like /home.aspx, it only happens when the url is /
Hope that helps,
Joe