Could I restrict to only use users from an existing database.

I like what I see with the Shopping Cart..
However I do have some questions to fit my project.

1. Could I restrict to only use users from an existing database. Change the SQL query to query another table of users.
   
2. Could I implement a discount structure per User . We have users that belongs to Accounts/Companies that has a certain discount.. % off MSRP
   
3. Enter the orders against the Account of the Contact instead of the contact (but use the contact as a reference).
   
4. Could I Change the view of price .. when not logged in then use MSPR (or hide price).. if logged in then use discount. Or could I require a login page to access the Shopping Cart, which then provide the discount and MSRP price.
   
5. Pre populate Billing information from an Account table.
   
6. Could Freight calculation would be based on product selected (instead of category).
   I am planning to use this for an existing Dealer network for a product Quick Ship Program . All payments would be done based on existing Account Payment Default. Like terms, Check , CC ...
   Does the product have some of above features out of the box or could I modify to make this work.