Apply discounts to multiple items & Call for pricing

I guess my question 2 fold.

• I would like to be able to apply discounts to an entire category at once, so I do not have to apply them individually to each product in that category.
• I would like to have a structure where I could discount quantities to a certain point, and have a display of CALL (Or something similar) for discount above a set point.
  Is this a simple thing to do? Applying discounts to specific item is simple, but very time consuming.
  And I have no clue as to how to make it so that once someone would like to purchase a large (Larger) amount then is normally purchased, they can call for custom pricing.

Thank you for any help you may be able to provide.

Kirby