Product and category discount

I want to make a discounted products page.

My first question is if there is some sort of plugin that I can use/buy to ease the process. I want to set a discount on a category and to all subcategories. I didn’t find any plugin that does that.

My second question is: how can I display discounted products on a page? I mean, can I put products on the page based on a tag or something? When I add a discount on a product to be automatically added to the promotions page.

Plugin, free or paid, doesn’t matter.