After marking the ruler I find they are mostly just under 5 3/4", some a little more wobbly than others, but almost square. As it's my first I'll just go along and see what happens at the next stage, learning process.
Had a play with layouts on the kitchen floor. I think I'll go with the random one.
Thanks for the comments on the colours, I can't take any credit as Aldi put the pack of 12 fat quarters together.