Is 5 sticks of butter correct? So 1.25 lb of butter?

Yes, you are correct. All that butter will make for a cookie that will melt in your mouth practically. And be sure you keep the dough cold until it goes in the oven. If the dough is room temperature, your cookies will flatten out in the baking.

Yes, at 4 oz per stick, 5 sticks make 20 oz or 1.25 lb.