ok,Sion
the type of challenge I love!!!..... because of the composition of the blocks there will be times that you want to make 4 petals or leaves that are at least approx the same color. Even with 'scrappy' you want some cohesiveness. Due to the seam allowances, you could be talking the equivalent of up to two charm squares - that is per color or section, per block. Picture a scroll that is 3" tall by 2" at its widest - you still need a piece of fabric that is 3 1/2 x 2 1/2" and there will be waste! You might have 4 of these color-sections per block. If you have more, the pieces would also be smaller, so let's say four. This would be 8-charm squares per block. Most will use less, so consider this a maximum. You can get approx 16 [4x4] charm squares out of a fat quarter, 2 blocks at a minimum, but since some of the pieces are small, you could probably accommodate the smaller pieces for 2 more blocks out of the scraps. If you considered 4 per fat quarter, you would still need 9-FQs. But you also need to find out if the person making the quilt wants a realistic look - which would mean a bit more of the green-yellow-rust-brown family for leaves. Most of us have a tendency towards one color family, so you may want to make more of one or two of your hand-dyes than others.
Take a look at my avatar - it uses the equiv of two charm squares of green and orange hues...5x10 each and a 3x6 piece of red for the red leaves and flower centers =3charm squares total.
Six is definitely NOT enough... 9 may be a conservative estimate as well - you need at least that.
Any thoughts on this?? Good luck
Gus