Nice tank!
Always wanted a 20 gallon long (although i would amke it an amazon tank with few plants an more leaf litter)
Is the reason you piled the gravel so high that you want the level to be low enough for the gourami? or did you want the plants' roots to have more room? either way be careful about using the gravel vac as if you disturb a thick pile of substrate like that too much, there could be ammonia spikes due to built up of waste.
I see you put flourite on the bottom and layered gravel ontop?
I think the gourami (snakeskin or gold?) might be not only lonely but also a bit cramped. havent kept them so take that with a grain of salt.
um, perhaps the giant danio (the blue one) is not a good choice as its really more of like a rainbow, needing more swimming space than a 20 gallon can offer. also those do best in groups as well. theyre very energetic as you can probably tell by looking at it.
Other other "barbs" are indeed phantom tetras. they'd like to be in groups of 5+
The tank looks good, and if you decide to keep the fish just the way they are right now, i think itll work out as long as you keep them happy water quality and food-wise.