Good change of plan for your first quilt! Smart thinking!! In the future, a good thing to do is make up one sample of the block you plan to use to help you plan the color positions - especially helpful for a Log Cabin quilt where you might want to have one side lights and the other side darks.

I don't usually buy pre-cuts so I can't help you there. I would expect that a Moda charm pack would have cuts the same size as another companies charm packs. And jelly rolls are pretty much the same size cut the WOF (width of fabric) throughout the industry.

If you look at a long row of whites at a fabric shop, you will see that there are bright whites, soft whites, grayed whites, etc. I think that "snow" is a softer white similar to my Chanteclere Vintage White that I love so much with my 1930s retro fabrics. I once read that the two whites were similar. Years ago I bought 10 yards of the Vintage online so I would have it for my 30's quilts. I keep it wrapped up in tissue paper, labeled, so I won't use it for other projects. If you want to keep your project made only from one white fabric, then label the fabric as to what it is exactly and be sure to only use the one white in your quilt.

Hope this helps!

Teresa