Website Form and Database

I need a website built that is based around a document that needs to be completed by consumers. The site will need to have more backend features than anything else. The whole premise is we want to send a link to customers and they will then click that opens up the form and then enter a code. The code will populate the sales persons info into the form. The customer will then need to digitally sign the form. Once the form is signed they will hit submit and the form will be emailed back to the sales person. Additonally a copy will be logged and stored in the site database. The main page to the site will be infomational and have some nice grapics. It will also need to have a admin page for users of the site where companies can sign up for the service and upload thier sales persons and company info thus creating the code needed for the consumer. The last piece is the site needs to have a sign up and payment page. THis is a basic overview. This is currently in the idea stage so suggesitons will be welcomed.