I love Moda Marbles, they are an absolute staple in my stash. I guess I would ask, what are your favorite colors?
Are you making quilt for a color scheme, like a bedroom or for someone else? Ask yourself what colors you feel gooood wearing.
Look thru quilting magazines and find colorways you like.
No two dye lots will be the same, ever. I keep navy, burgandy if I can find it, red, and I love turquoise and the yellow, I like the
blue as well and the purples are great.
The advise I heard once from one of the qulting queens years ago was if you LOVE a fabric buy either three or six yards of that fabric. With marbles, the colors are pretty close so I
wouldn't worry about it.
If you just want a stash, wait for a 30 to 40% sale and buy what you can afford. Now I have a huge stash but I live 40 miles from a town and a lot more from a city.
It makes more sense to do one project at a time, good advise that I never follow. I usually have 3 or 4 going at once and go back and forth.
The other thing that influences your choice is what is offered by mfgrs, seasonally. If fall, autumn colors predominate and so on.
Make a start by checking a few patterns for quilts and buy what you would like to see in that quilt as far as yardage.
I don't buy less than a yard and I usually need more but if you have a reliable source, buy what you can as you go.
BUY WHAT YOU LOVE. Good Luck.