Custom user dashboard in django
This sounds like a situation where you want the functionality to be loosely coupled to prevent headaches down the road, so I'd go with option 3.  Leave the admin for the admins and create a new dealer app for the dealers to go to, with a regular view/model/template that they'll be required to login to see.
I have a system that has two types of users with different privileges, the first user is the admin who can access all objects from the database, the second one is a dealer who can only view information pertaining to them alone.(There are many dealers)
This is how the system iworks: the admin creates a coupon code and issues it to a person (already done) then that person goes to a dealer who is supposed to check if that coupon code exists.
when a dealer logs in he is supposed to be redirected to a dashboard that has the number of items he has sold and to whom. To sell a new item he needs to check if that coupon code exists and if it does then access a form to fill in the item details(I have a model for issued_items)
How would I implement a custom admin page for the dealer without affecting the admin dashboard.

I created a dealer with super-admin and changed his permissions so that he is only able to change specific models, problem is, the models appear with all objects in that model even the ones by other dealers.
I have thought(not tried yet) of creating a view,and a template and redirect login but if i do this then i override the admin 
(not so sure)Probably create a new app for the dealer???????