more universal discounts

I saw on products you can set individual discounts, so you can have a 10% off sale or what not.

Is there a way to have a sale on multiple products all at once?

I saw the coupons and they allow that, but need to be typed in. Is there a way to automatically apply the coupon for everyone?

On the coupon page there are check boxes for all those products, but if there's a lot of products, could we get a category list as well?

Do coupons compound on each other? Or is it one at a time? If someone types in one coupon, then types in a second one, does it still deduct the uses for the coupon for user and customer?

What is the "total amount" box? I went to look at the docs for that, but it was the only definition that was missing, lol.