Login Features

i am currently building a website for the company I work for and while this site has not gone live yet we are inching closer to being finished with it. As of right now I am trying to figure out the best possible way to integrate a login feature that would allow people to register for user approval for access to additional content for this site. Currently we do not sell directly to consumers and are fitting a wholesale “back-end” ,if you will, for our wholesalers to be able to view and purchase product. I am fairly new to the WordPress game and would just like to know if there is an optimal way to be able to have my users register and then have me be able to allow or deny each user. I also need a log in feature for the approved users to be able to gain access to the additional website content. I have been looking through plug-ins, but I’m not sure would allow for the best interface for both my users as well as me for the administration editing back-end. Any help, advice, and information that anyone can supply would be greatly appreciated.