Web 2.0 stle sign-up page with external DB integration

I have a regular Joomla CB website with only sample content on it, which can all be reomved/hided. I had a freelancer a script developped for me that attributes to every new user different coordinates on Brazilian map. Thats the main idea on my site. So there is a page where is a map and shows icons od each user on the map. Thats working fine and shouldn't be changed. What I need is a simplified look of the website, web 2.0 style with big form field and ajax. I got an external db from a petition. The people who signed it provided their name, email, id card, city and state. (always from Brazil) So I want to invite them through an email with a special link. When they come to my site their name, email, city and state should already be on screen and they should only create a username and password. After that they already get logged in and get access to that map I wrote about before. Beside that I want my website to have the sign-up form on the home page beside some introduction and a simplier login form somewhare on the right upper side or so. The user should first provide his e-mail. Instantly an Ajax script will check the external DB and see if this email is already on the petition (external DB) or Joomla. If its on that DB the visitor will be notified on screen that this email exists and that he should type in his id card number in order to verify him. If it right, the ajax will fetch his name and proceed like before, just asking for username and password and then login as before. If the email is new, normal sign-up fields load below, where the user must provide his name, city, state. I dont want to ask as many thing as CB wants too like address. These things may be filled in "update my account", but shouldn't be asked on sign-up. I created a graphic where these things are more exlained. This website mus really be vert simple and web 2.0 style. big fields. clear layout and intelligent.