Customized Wordpress plugin

I have a wordpress based site that I want to modify the registration process to. There is a plugin by [login to view URL] called the Socialize plugin that allows you to accept registration credentials from various sites like Facebook and Myspace. I would like users to be able to register for my site using either Facebook, Myspace, or normal registration. The tricky part is my site user are split into two categories. Category A is your typical fan that would like to register to receive emails, leave comments, etc. Category B user is a band or musician that would like to register to also receive emails, leave comments etc, BUT will also be part of a special group that inputs extra information on the registration process, as well as being included in a "Musicians Database" listing similar to a members list. For both Facebook and Myspace registration processes I would need to add a call to find out what type of user is logged in and if the user is logged in as "band" or "musician" types then send you to step 2 of the registration process to collect extended band information like email, band name, zip, page urls, etc because you cant store that info pulled from FB or MS. If the user is logged in thru FB or MS as a regular user it would take you to a different step 2 that would have different extended info to collect. As far as using the [login to view URL] plugin as a base, I wouldnt mind it being a fully custom plugin that does basically the same thing as the Socialize plugin, but I figured this would be a good base as they have all the functionality already in place. The end result should be that a musician can come to the site and register to be listed in our musician database by being logged into either their myspace or facbook band pages and registering that way, or using the typical registration form that gives you a choice to register as a regular user or musician then showing the correct form. This must also work with the other plugins i am using currently on the wordpress install.