I think you need a total of 150 watts for your heater. Since it's a long tank, I'd use two 75-watt heaters, one on each end of the tank. I place mine vertically or slightly slanted but I keep the dial where it's easy to read and adjust.
If you are using fake plants, you don't need Eco-complete. It's a very good substrate and the only one I use. But it is somewhat expensive and it would be "wasted" if you're going to have fake plants. The moss doesn't have roots so it doesn't need Eco either. You could get regular black Estes gravel if you like a black substrate.