Substrate question

[Cowboy]

I am setting up a 75 gal tank with a 4X65 pc lamp, ehiem 2215 canister filter and a carbo plus CO2 system. I would like this to be a very heavily planted tank. My question is regarding the best substrate to use. I am eyeballing the Seachem florite right now, but I thought I would throw this out to you all. What do you think is the best/most cost effective substrate? Futher, should I use a substrate heater to promote growth?

thanks,