I have used Jelly roll size (2 1/2") with good results, but I know of no reason why you can't make the squares larger and the strips thicker.
How big do you want to make the quilt and curtains and how many blocks do you wish to make? That's the determining factor.
I've made a 1" quilt square into a 100" king size quilt when I wanted to have a "Flaming Star" king size quilt (lone star pattern in multiple colors). Essentially the larger the block, the larger the pieces can be. Why not decide on the size you want and work the pattern backwards to see if that is what you wish to do?