Wordpress multiple user accounts

We need to implement a user account systems in our wordpress webpage: www.forecos.cl. To display private content. characteristics: 1. Create a Subtle Login button in the page 2. Password recovery system 3. There will be two kind of users: User A - Client 1, Client 2, Client 3.... They would access just to the content related to their account. But *can not* see the content of the other clients User B - Master User. They would access the hole private content in the webpage, it means they will be able to see all the private content of every client webpage users. 4. Don't allow visitors to register, we need to manage new user account creation. (it is necessary to indicate how to do that). There are many plugins that resolve such functionality, but i can't resolve the problem by myself.