A GH of 120 (about 7 dGH) is soft approaching medium hard. As redchigh says, calcareous rock will raise this but depending upon the rock type it may be slow or not. Not a problem for livebearers. Vallisneria loves hard water, so that is good too, and it easily assimilates carbon from carbonates (higher in hard water) so the limited CO2 from the few fish will not be a detriment.
Vallisneria frequent looks like your original photos for a few weeks, so at this stage I would not be concerned. The existing leaves will not improve, but new growth will (should) be lush and green. I don't know Flora Grow or what's in it.
A word on the "stuff" going in the tank. StressCoat is a water conditioner on its own, so I would only use either this or your other water conditioner which you don't name, but not both. Overloading the tank with chemicals is something I do not advise; regardless of the claim most conditioners make that they can't be overdosed, it makes sense not to use more than necessary. I can't help but think they must have some impact on the biological system.
StressZyme I assume was used to "seed" the tank at the first. I would not continue this product at all. The claims it makes for breaking down organic compounds is something best left to nature. Speeding this up will increase ammonia, so this is somewhat at cross purposes. As the tank has been running 2 weeks, with very few fish and live plants, I would not use StressZyme further.
Just one good conditioner, and the fertilizer (never exceeding the dose on the label) and you're set to go.