What is the perfect sand bed?

I'm in the middle of a total break down and I will be adding sand to the display tank.

What is a good size sand bed as far as INCHES for a 210 gallon reef ready tank?

What is not enough and what would be to much?

I have 3 bags 40 pound bags of Seafloor special grade reef sand and 1- 40 pound bag of fiji pink.

Debating about mixing it all together or just using the 3 bags of reef sand.