When I made mine, I tried to buy most of my colors all at once. Then later found more fabrics that I liked more than the once I had. So I would suggest you decide what you want the center to be - I chose yellow. And from there you buy fabric as you go. It does help to keep pieces of what you have so that you don't buy them twice. I did a white path through mine. They are rather addictive - I have enough flowers left over the make another full size quilt. I have been looking for a green to use as the path, just haven't found the right one yet.
What size hexagon do you plan to use?