I'm really attached to this idea now - thanks for all the food for thought guys.
I've found a 130 watt 24" coralife light which I'd like to hang above the aquarium.
My plan is to use a 29 gal tall (30" long vs 24", same depth of 12") ontop of the stand with the 20gal from the images resting on the lower shelf. I'd like to then have an overflow box siphon water to the lower tank through a 3.5' long 4" PVC drip/canister of pure biomedia into the lower tank which would act as a sump / shrimp breeding tank. I'll have a low wattage light and grow mostly java-moss, a dark substrate will be used to enhance coloration. I figure some of the fine mechanical debris from the main tank will be eaten by the shrimp, and be filtered / caught by the java moss - and the shrimp will have the most filtered / stable water directly from the canister. The larger water volume will also mean less PH shift / nitrate buildup.
The top (30x12) tank will be a low-tech dirt with miracle gro organic choice / worm castings / clay with a "filter sand" cap. Plenty of the bogwood. Right side planted mostly with anubias / java ferns. Left side planted with a variety of stem plants.
Additionally, in the rear, right corner I'd like to make a small raft and float baskets of hydroponic media to grow peace lillies and/or pothos. I'll run a small waterline to the top of the driftwood to trickle down. I'll take the advice on moss and cover the log with it.
Since the window receivers early morning light, mostly in the red spectrum I think I can get away with an actinic bulb and a 10k in the suspended fixture.
Algae is my biggest concern.