Layering vs Mixing substrates

[magnosis]

I have different types of substrate accumulated in my basement and want to add it all to my 55g tank.

I have:
- 2 parts flourite red
- 1 part flourite black
- 2 parts flourite black sand
- 1 part eco-complete black
- infinite plain gravel

Should I mix it all up together, or lay down as layers (in what order) ?

From what I know I lay gravel on top of everything to facilitate circulation of water/air through the top soil... I think.