This is awesome. We are not set in stone on the laptops. For a scalable business model, it is safer to rely on donations. Rasberry pi will also require a bit more peripheral devices i.e keyboard, mouse, monitor. But if we start getting Rasperry pi donations, totally. The kids will learn the in and outs of a computer with that kind of set.
Used laptops are not that more expensive, but they are beefier, the UX is better.