Need help to build a list,.protect a page and shows only excerpt on homepage

Hello guys I need help to customize my word press site
I have build a site using Mantra theme in which I offers certain bonus for buying the product through my affiliate link.
I have a plugin which allows user to enter their click-bank receipt number, if the buying is genuine it will redirect them to the download page.Thing is I need to collect their email for building list, before they download.
So please suggest any free plugins which will do the job. It should be like this, when customer enter genuine clickbank receipt number they will redirected to a sign up page. From there to the download page when they enter email id in a sign up form. This plugin should helps to collect the email ids.
And also i what to know
1)how to protect the download page form leechers
2)Plugins which make post excerpt in homepage
Hope i make it clear. Please help…..