The Foundation or Foundry discussion has come up quite a few times in the past. I don’t see the need to start another.
If you do a search, you’ll find some older topics, but here is one to get you started. Foundry / Foundation / UIKit / Bootsnap / Blueball Freestack: Which Framework to choose?
Both Foundation and Foundry rely on stacks (included) to build the pages. To be able to use stacks from Foundry/Foundation, you need the main Stacks plugin which is a separate purchase. So you’d need to buy Foundation or Foundry and then the Stacks plugin on top.