Controlling SQL Access In .net - Revised

I have windows application (Basically a accounting system). I want to use either SQL authenticaion, or Windows authentication for my users of the application (Basically each db user will have their own account in Users for that db, so I can have sql control the access).

All access to the db is via stored procedures, but I want to have a set schema for each user type:

Supervisor
Manager
Data Entry
etc.

All with a predefined access to the proper stored procedures(So far fairly simple).

In addition to this I want to be able to set the specifics of that user in my .net application via a interface (so a user by default will have the pre-defined schema, when a supervisor opens this interface, they can add/remove access to other stored procedures)

Here's the issue. Is this the proper methodology to achieve this, because it's quite of bit of programming work. I don't want to do it then need to re-due everything.

Also should I use Windows Authentication, or SQL, or have a completly seperate table in the DB where I do manual authentication then have the .net application restrict the access?

Any help or comments on this approach will be helpful. Also ifanyone has found any articles or information similiar to what I am trying to accomplish, please point me in the correct direction.

Thanks.