ad 2) C. wendtii does best in better light conditions. Your tank is a compromise.
ad 3) With gardening I mean the idea that a normal aquarium needs many growing plants, a good idea. Nevertheless, you must distinguish between the structure of a natural biotope (with a huge bottom and rather little amounts of flowing waters) and a tank. You cannot copy that by having a bottom layer a bit thicker, an inch or three inches. Your ideas of plants as filters are very good for normal aquaria, but not for specialized blackwater tanks. Of course, you can try intermediate ways, but you will not meet the full requirements, neither of the Paros, nor the plants.
ad 4) good!
ad 6) some do, but others not. In most natural habitats the pH is lower (see literature!). What you intend (and many of us, admittedly) is a compromise. We are caught by the images in our head and the wish to see nice green plants in our tanks that should look nice and cozy. Walstad was a huge progress in America compared to the very unnatural and ugly tank-models that were in usage before. But she offers no recipe for a Paro-tank. The only thing I want to say is: Paros in their home-habitats do not live in underwater gardens. Mostly, there are only grasses growing at the side and hanging partly into the water.
ad 7) I would love this too. But experiments show that nearly all of our traded shrimps don not flourish in nearly destilled water with low pH. A friend of mine had some success with a rarely traded small species, but again at a relatively high pH and a mineral content near the border of Paro-conveniance.
I am sorry, but your wishes are those of many aquarists. Nevertheless, the structural differences between nature and the tank are important. We forget this with our usual aquaria, In this case we see them very clearly. Anyway: You can continue to make compromises, of course, I do it in some of may tanks, too. But we should see them as what they are: compromises. If you want to breed your fish as your dominant aim, then you should give them an environment which is as much as possible constructed for their need and not for yours.