24's ok till you want to flower. It's really preference there, 18/6 is used because of heat and electricity issues. I've never had problems with 24hrs light in veg...

As for the leaves, wide ones like that are usually indica-indicative. Lol, just wanted to say that.

And the mirror's not going to reflect too much really, better with flat white paint. Reason is that the actual reflective part is the backing so the light has to travel through the glass before bouncing back so it's having to penetrate the glass twice.