What is the source of nitrates?
Tap water? May or may not have any other nutrients. I would dose P, K, and micros.
Fish food? Usually has a fair amount of P and Micros, but is usually lacking Fe and K, so I would dose those 2, and perhaps low doses of P and Micros.
Watch what happens to the NO3 when you start dosing. MAYBE the plants are growing OK, but will grow better when you feed them something that might be lacking, then the plants will start removing the NO3 faster.
GH so high suggests there is plenty of Ca and Mg, so do not dose any form of GH booster. On the other hand, the GH test is one of the first to fail. Is it taking more drops to turn color because it is getting old?
KH is carbonates. Carbonates are used by some plants, but only when CO2 is too low. Carbonates are used by the nitrifying bacteria. I would dose a little bit of carbonates (baking soda or potassium bicarbonate) to get the KH perhaps to 2 degrees, and test to be sure it does not drop to 0. 1-2 degrees is fine, but sometimes problems happen if it is allowed to drop to 0 degrees. Some substrates will remove carbonates from the water. Dosing to counteract that is a good idea.
Do you have any substrate fertilizers such as tablets? Gravel will not hold fertilizers like a substrate with good cationic exchange capacity.
What I would do now:
Practice with the fertilizers, get used to dosing at a low level. See how the plants respond.
After Christmas, when you are ready to make this a higher tech tank get a better substrate and you will have the fertilizers and CO2 ready to go.
As for the light, I would generally prefer to have more than one color of bulb. That way, each offering different wavelengths the plants have what they want (hopefully) and the tank looks right by our eyes.
