I would get a DC pump, The new range of DC is much better then pumps like laguna etc. I got a 10 000 LPH (2600 GPH) with 5.5M head @ 85W for 300$ (maybe cheaper in USA) made in the same factory as Laguna. so far it works a treat on a system just a bit larger then yours.
1. what do you think of the concept: Cant see any issues. I run multi tanks off 1 sump and find it great just QT fish. 1 pump would be ideal energy wise but back up wise having 2 is a better idea. I would run one into a UV/Pond filter filled with mech to fine polish the water.
2. heating : I find its easier/safer/cheaper to heat a room when you have 1-2 big tanks or many small tanks so I would vote for heating the room but it creates a bit of a task. If it came down to the heaters 1 big aquaponic grade heater would be best. look at it this way if you have more heaters you have a higher chance of a malfunction and all your fish burning to death but one larger heater will be best imo.
3. Lighting: leds? MH? T5´s?. LEDS or t5s. MH produce amazing lighting but will heat the water and pump the power bill "super high". T5s are nice you can create some cool colors with a few but tube replacement can cost money so I would run some LEDS, less heat and power + longer life and shimmer effect!! I use some cheap 120W china ones they are quite common down here. One on my 7x4x2.5 and it works great.
Just make sure you aim to save money long term with the hardware you buy, big tanks can drain too much money.