If you do it to the side, it will be easier to quilt. But if you do it, say in blocks of so many charms, it might be hard to match your seams up right.
They would match up no matter how you put it together with pressing the seams open. I really don't know how the quilting would be on that.
I've never pressed seams like that. Always to the side for me.
Maybe someone else has done it both ways and can let us know.
Would love to have you sewing along with us.