Your e-mail address is only used if you ever need to reset your password. The budget amount is the *total* amount you can afford to pay towards your debts (all of your minimum payments plus whatever extra you can afford). It needs to be *more* than the total of all of your minimum payments for the debt snowball to work. You can always change it later anytime you want. Here's some quick help if you need it.
Try out Undebt.it before you sign up by taking it for a test drive with the demo account. It's pre-populated with a few accounts so you can dive right in and see how it works. The reviews & testimonial page shows what others are saying about the site.
Take a Test Drive Reviews & Testimonials