Yes, you can use those felt squares for a felt board, those are acrylic felt squares, and yes, they are good enough for felt board stuff. I've used the fabric on the bolt to get a large enough piece to cover a corkboard (they are relatively inexpensive). I used spray adhesive to adhere the felt to the board and it turned out nicely. I used a light blue piece for sky, and a green piece to make grass.
I save the better quality felt for other felt projects, but for the felt board, this kind works fine. I've made shapes from cookie cutters.
Joann's has the large bolts of the acrylic felt as well as the squares.