Magento coding modifications

I am setting up a Magento site with multiple store views/themes for multiple domains and a single unified core magento installation. I have been able to get the cart working so it shares products added at one domain to be carried across all carts(stores/domains) I have also setup the unified registration so no matter which domain they register at it is working to register them at all HOWEVER this is where you come in at TASK 1 Create a multi step registration form 3 steps will be displayed in a cookie based popup on landing pages ((i already have this done)) so we will be adding the code to this. I want this either built as a exstension or packaged so i can re-use it at my other sites on other servers that also use this parts finder system and packaged for me to install at my other sites along with the dependencies the pop up/parts finder/core files etc. Step 1 enter email upon doing so it will create their account and a email will be dispatched containing a system generated password which of course they can edit. Link in email to login page etc. naturally a email template for it after entering their email they will have 2 options {Continue}or {maybe later} if {continue} they will be taken to (Step 2) if {maybe later} then they will be logged in and directed to the edit account page Step 2 here they will fill in their {{then year make model engine}}from a drop down list that will pull its info from the sql we use a parts finder extension so it need to pull its info from that extension sql entries for the {{year make model engine}}. at any rate this year make model selection will be stored as a customer attribute which they should be able to edit as needed or add additional vehicles from their my account page. {Continue}or {maybe later} if {continue} they will be taken to (Step 3) if {maybe later} then they will be logged in and directed to the edit account page Step 3 here they will fill in their first name and phone number so they click submit and it will register and log in and sent to the my account page. {Submit and login} ->they will be taken to edit account page - additional noted factors this {{year make model engine}} tool is in the header and product pages of the site once they log in there should be a button they can click that will set it to their vehicle "use my saved auto" TASK 2 I want it so once they log in at one of the stores it logs them into all of them and they only have to log in once regardless of which of the domains they log into. currently they have to log in every time they visit one of the other domains meaning everytim they switch domains they have to log in again. This could be me not understanding the setup and as simple as setting the cookie to a specified domain then they would be logged into all of them when they login to any of them? if it s anything more than a simple setting that i missed then I would like this created as a exstension or delivered as a zipped package which i can extract on the server it should have admin side controls at least a on and off switch :) if any coding has to be reconfigured to add additional domains beyond the original 5 them there should be a function in the admin side for adding editing deleting etc.