I've used each and currently have tanks running with all that you mention except sand. All will grow most plants. Flourite and Eco Complete are essentially the same, only EC doesn't have to be rinsed 700x. Flourite seems a bit more jagged in my own tanks, but this is far from scientific and it could well vary from batch to batch. To save myself the rinsing alone I'll go with EC every time going forward if setting up with inert.
Stratum is an aqua soil, in case there was any confusion there. I've yet to see any indication that aqua soils quickly turn to muck if using low KH water and no rocks etc. that will leech carbonates. My oldest tank using it is only 4ish years set up, but so far no change other than losing some over the years of substrate vacuuming. It's very light and every water change there's a couple of tablespoons of sediment in the bottom of my shop sink that I don't get from heavier substrates. It obviously has a life span though, and the others will last pretty much a lifetime. Do bear in mind most aqua soils will create a soft acidic environment that's not suitable for every species.
I agree with Dave that dwarf hairgrass is probably going to disappoint in low tech. Pygmy chain swords might be a better option, maybe even monte carlo. CO2 tabs "work" but that would be expensive and time-consuming long term. DIY methods seem to have come a long way since I last tried, but on a tank that size I'd be inclined to use pressurized or just go low tech.
Nothing good happens fast in an ecosystem.