Unless you live in Alaska or Siberia, you don't need a substrate heater.
Eco-Complete is the best commercial substrate IMHO. It looks great, and it's saturated with all the goodies that plants need (even 4,486.78 ppm of titanium!), not to mention that it's bi-modal, in that it contains different grades of thickness, from sand gradually to gravel-size chunks and it requires no pre-washing. It's jet black. I mean JET black. If you're thinking about using that Home Depot sand, forget it. Don't even bother with the E-C becuase you're substrate is going to look like

and you'll waste ur $$$. You'd be better off going with sand and laterite. Anyway, I picked up some black beach sand when on a day-trip up PCH. Honestly, I thought this sand was going to match the Eco-Complete, but it turned out to be way lighter (you know, sort of grayish comparitively) but it would still look good mixen in with the E-C because it was really dark. Mix it with either Onyx sand or just some black sand, that would be the best IMO. E-C and Flourite???
Maybe, but that will cost you just as much as another bag of E-C.
Suggested depth is 3" or 2 lbs/g. So it's basically one bag for every 10g.