Filter: I'm thinking either 2 Aqua Clear 50's or a Fluvel 305
I'd say go with the Fluval 305 with the bottom tray full of pure Poly-Fill for extra mechanical filtration, you can get at Walmart or a crafts store. The other two trays can both have BioMax for biological filtration. Once the tank is cycled and establishedThe Poly-fill would need to be changed every 2 weeks, but other than that, you could go a month between filter maintenance.
substrate: 1.5-2" flourite (bottom layer) and 1.5-1" aquarium gravel
This sounds fine ... as an alternative, you could do Pool Filter Sand as a bottom substrate for roots to hold onto and then do gravel.
The heater and lighting sound good to me .. maybe another member with more experience can give an opinion.
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.