The general rule for space is a MINIMUM of 1 square foot per bird. There are commercial breeders who will say to cram 3 birds/square foot, but personally, I think that's rather cruel. My birds have 2-3 square feet per bird.
You will want to check with your local ag department about whether or...
Coturnix come in a LOT of colours. Harlequins are a different species, and I would recommend starting with coturnix if you want eggs and/or meat. Buttons come in a lot of colour varieties too, but they are more ornamental or pet quail.
I definitely would not house coturnix and buttons...