Login & Registration Help

I am building a site for the company I work for and would like to implement and change some things on the login and registration pages. I am using a plugin that customizes the look of the pages, but there are some technical things that I would like to implement, but not sure how to make them happen. First I would like to have it when the user is logged in, they be redirected to a sub-domain as the users that will be logging in are going to be able to viewing a wholesale portion of the site, where the public will not be able to view and or purchase. When they enter in the correct information and click the login button I want them to be redirected to the sub-domain, but I am not sure how to, or where to, make that happen. Also another question with this is being able to change and add labels and inputs to the register page so I am able to get more information from people who wish to apply for site membership. Ideally I would like to be able to police who is allowed membership, per request from my employer, but it would be nice to also be able to get some additional information, if possible. I am not super familiar with php, but if that’s what I need to do to be able to get the desired look and functionality for my site then I am willing to tackle that. Please, any information or advice that anyone has about getting this accomplished or plugins that will help, I would really appreciate the hand.