Thanks for the detail, that helps us. First on the stocking, this is not what I would consider over the limit, and neither is your feeding. At this stage I would do several water changes, maybe 1/3 one day, and another 1/3 the next day, then 1/2 the next. This should lower the nitrate significantly. Test the nitrate daily before each of these changes, then maybe alternate days until the next water change. Stay with 1/2 the tank every week, unless this doesn't work.
As for cleaning the substrate, normally I don't as this is a prime source of nutrients, especially carbon for plants. The majority of CO2 in an aquarium comes from the decomposition of organics in the substrate, and removing these is only going to lessen the CO2 available for the plants. However, I do a surface clean in one or two of my tanks, simply because each tank is biologically unique and these need it not because of nitrate but one tank for some reason will periodically develop cyanobacteria, which is due to organics, so this seems to work. But in your case, initially anyway, I would do a substrate clean with the water changes but nothing too drastic. Open areas, and not digging down much.
Now to plant nutrients and fertilizers. First, I would not use Excel. This is a highly toxic chemical; Seachem call it "pentanedial," which is another name for glutaraldehyde. Used according to directions, it is said to be safe for fish, but it will kill some plants (Vallisneria, Anacharis and some others seem especially sensitive to this chemical). If it should be overdosed, it can kill all plants, bacteria and fish. It carries warnings on use from the government, not to get it on skin, breathe in fumes, etc. It is used in hospitals to disinfect, in embalming fluid, antifreeze, and to kill bacteria in ship ballasts, among other uses. I don't see the need to add this chemical to a fish tank. Though it can kill some algae, brush especially, but there are safer ways to deal with this.
I use Flourish Comprehensive once a week, and Flourish Trace once as well. I have very soft (near-zero GH) tap water, so everything has to be added. In two tanks I also use Equilibrium to raise the GH from zero to 4 or 5 dGH, solely because the larger Echinodorus will not have sufficient calcium and magnesium without and they die. The plants in the other tanks do fine without this.
Plant nutrients occur from fish foods and water changes. The GH of your tap water is something you should know, but I will assume it is likely not low if your Wisteria is managing. [Wisteria doesn't last for me, unless I add the Equilibrium.] Flourish Comprehensive once a week, after the water change, is not likely to cause any issues. There is very little nitrate in it, as it is intended to be a supplement, to simply add a balance of nutrients that may be missing otherwise. Seachem says the limited nitrate in Flourish will not add "nitrate" per say, so I wouldn't worry. However, it needs to be regular. Dose the tank at the level on the label just after the water change.
The enriched substrates like Flourite and Eco-complete ironically do not help plants much, at least not in my experience; you still need to use liquid fertilizers just the same. I had Flourite for two years, then replaced it with play sand and after a few months the plants are actually doing better. It is also sharp for substrate fish; I had to remove my corys from the Flourite tank as it damaged their mouths; over sand they have healed fine, though the barbels didn't grow back.
Algae. Anubias is prone to brush algae, because this plant likes shade. Floating plants would help here. And they have the added advantage of being heavy feeders, so they would take up even more ammonia/ammonium, thus further reducing nitrate.
Let me know if anything isn't clear, and keep us posted of progress. Nitrate of 5-10 ppm in a natural-method planted tank should be the max.
