OK, let's start with the motherboard. The Asus B250 Mining Expert is a beast of a motherboard, capable of having 19 graphics cards connected to it. That's a lot. The board isn't new -- it was released in 2017 -- and it is finicky when it comes to setting up (it needs a specific layout of AMD and Nvidia graphics cards),
Asus has published recommend GPU layouts for 19-, 13-, and 11-card for this board, and while other layouts might work, I recommend staying with what the manufacturer suggests, as veering away from this is a recipe for a serious -- not to mention expensive -- headaches.
Yes, prices are soaring for this motherboard, but that's part and parcel of bitcoin mining. If you want something priced a little more reasonably, then you could take a look at the Monland B250C BTC Mining Motherboard. A lot less powerful, but a fraction of the price.
Note: Asus recommends running Windows 10 with this motherboard.