How much dead rock per gallon? Lighting for cycle?

[SeaSerpant]

I have a 120g aquarium that i'm going to put 5 bags of sand (30lbs each) and seed it with live sand. I'm going to use dead rock with a bit of live rock instead of all live rock because i can't afford that much!

So here are my questions, How much dead rock per gallon? because i heard that when dead rock becomes live it weighs more than when it was dry.

And do i need lots of lighting for the cycle? because i don't plan to get the light until a bit later. but still plan to have some light over the tank!

Thanks
SeaSerpant