I have one live Joomla website which my other domains are redirected to.

1) The script I need will “read” and parse the URL which the user came to, and compare it to a record in the database. It will then return another field from this record and add this data to <fields> in the main website… thus making the experience unique and personal to all users no matter which domain they visit from.

2) The programmer will add an extra field to my DB tables (with user-generated data) that will log the domain from which the domain is added. Some of the scripts on the front-end will have code added so that if user is from DomainA then user-generated data from DomainA will show first.
3) Also need the user name to have the domain automatically appended to it. For example, there can be multiple users who sign up for "mary" if they sign up at separate domains, because the full user-id becomes mary(a)domain1.com, mary(a)domain2.com, and mary(a)domain3.com.