It also depends on the type of quilter you tend to be. Myself, I usually make scrappy quilts and like to have lots of variety in a quilt. That being said, I have a ton of UFO projects. Every new pattern tempts me to try a block of it to see if I can put it together, like a puzzle that needs to be solved, tackled. Someone else on here mentioned this mindset. Hopefully, you are a starter, finisher. I'm easily distracted!!
Now to what I was going to suggest to you. Once you consider your own quilting style, personality, that will influence how much of a particular print that you should buy. I would never end up using 6 yards of black, esp. a solid black. I know I have at least a yard of it and noticed that it picks up lint something awful and it's a good fabric. I have also search unsuccessfully for more of a fabric that I had just bought a FQ or remnant of and never found more and had to substitute another. Since I like scrappy quilts, substituting isn't a problem.
Anyway, your own personality will dictate how much of a fabric you will want to buy. As I said, I'm unlikely to use a whole bolt of any fabric unless it is a neutral for a backing and even then, that's a lot for me to buy. So, consider everyone's advice and enjoy shopping. A quick note about what I'm doing at the moment.....my local quilt shop has a little basket of remnants packed in ziplock bags. Some might have 8 remants in it of coordinating prints or it might have 2 pieces of similar prints, etc. A recent purchase was of a red Civil War prints that I just love that was 1/2 yd. and another smaller piece of something that matched. This is a gorgeous CW fabric that I had not been able to find elsewhere and the little packs are only $3.00 so it was a great bargain!!
Enjoy collecting!! Brenda