justflyingin

I don't consider buying it on sale, "jumping the gun" but it definitely depends on your own personal style. For example, if you buy ingredients for Thanksgiving or Christmas dinner 2-3 weeks before you actually prepare the meal, is that too early, or do you want til closer to the date, so that you know for sure all that you are going to fix?

I'd buy it on sale if you find what you like. Then you will have it on hand when you are finished with this top.

MadQuilter

Since you have the front colors defined, there is no problem buying the back fabric. If you know how big the top will be, the backing amount should be known as well. I would go with an understated back as well - similar to the front. It's pretty and daring for a beginner. The good news: You will be an expert in set-in seams.