I love the pattern made with only 4 fabrics. It's downright stunning.
I am not a beginner and would hesitate to use any directional fabric with this particular pattern. It's going to require that you figure out how you are going to place the blocks before you even sew them. I would just go ahead and substitute another fabric. As for how many yardage. This is how I calculate it...others may do it differently.
finished size 70" x 70" = 4,900 square inches
one yard 36" x 40" = 1,440 square inches
divide sq yd into finished inches 4900/1440 = 3
Because you are going to lose some to seams, I would buy about 1 yard of each fabric. I don't think this would allow enough for the binding, but am not sure.
I am so glad you asked about this pattern. For the guild I belong to, our challenge this year is Black & White and red all over. There can be other colors added to. This is going to be the one I make.