I just set up my 7.5 cube with MTS. I know you don't have to screen it, but I would highly recommend it. I rinsed mine quite a bit, let it dry, repeat. On the last dry cylce I used window screen to get rid of leftover junk. There were still bits of wood, and other debri. I was left with a fine powdery sand.
From there I just added enough water to make mud and placed it on the bottom of the tank. Capped it with sand, I used sand from HD that is used for setting pavers, it looks ok, but with any luck will be covered in plants so..
There is a sticky at the top of this forum that will answer all of your questions.
I'm by no means an expert, but there is a lot of info on this site that helps.