Advice for semi-planted aquarium?

I'm making planters out of cross-stich sheets and nylon thread, then
when I have the right shape using aquarium silicone to cover them in
either aquarium gravel or river rocks (some of each.)

The substrate in the planters is going to be laterite mixed with
vermiculite, with pond fertilizer tablets (if I can find them) and each
planter will be 3-4" deep. 160 watts over a 55 gallon aquarium. I'm
planning on a few massive Amazon Swords and some other hardy plants.

Does this setup sound feasible? Any advice would be greatly
appreciated.

Thanks in advance,
Jamie

-cross-posting on req.aquaria.freshwater.plants