You asked about calculations, to quilt a twin at 1/2" spacing for a design with minimal thread build-up, I need 4000m of thread. I then do math from there & build in a 500m cushion. So for a queen I'd want 5000m of thread just for the quilting. If I'm doing a lot of pebbling or such, I'd want to add in more. I'd try to guesstimate what percent of my quilt used microquilting or thread build-up and then multiply that by 2 (to account for going around an average of 3x). For example, if I was doing pebbling on 10% of my quilt, I'd take 10% of 5000 (500) and multiply that 2 (1000), then add that into my original number (5000 + 1000 = 6000). Yes, I usually end up with 100-200m of leftover thread, but I'd rather a bit too much than not enough.
If I'm doing 1-1.5" spaced quilting, I would start my calculations based on 2000m of thread. I really don't quilt much farther apart than that -- never more than 2" apart -- so I can't really speak to how much thread you'd need for minimalist quilting.