Modelling products along with their attributes and discounts for an e-Commerce database
regarding question 1):
A table with the following fields
1) date ,to set the date-from which the discount is valid
2) product, to define which product we are talking about
3) discount_type, i.e. 1=percentage, 2=how_many_product_for_this_price, 3=price
4) percentage, needed for discount_type=1
5) quantity, needed for discount_type=2
6) price, needed discount_type=3

Example:
If you have this data (I will leave out date for simplicity):

product, discount_type, percentage, quantity, price
1, 1, 0.5, null, 42
2, 2, null, 2, 42
3, 3, null, null, 25


product 1 has a discount of 0.5*100 = 50%, and a price of $42

product 2 can be sold 2 for the price of one, so 2 for $42

product 3 has a discount for $25