I'd like to just add a couple things to the good advice already posted by other members.
Substrate--by Fluval do you mean Flourite made by Seachem? Or something else? I'm asking because Flourite is a bit rough if you intend substrate fish like corys; I have it, but I removed the corys from that tank because of this. Playsand is a very inexpensive option, if you have it around 1.5 inches depth overall. With substrate plants and Malaysian Livebearing snails, it will not compact.
Fish--I would not introduce gourami into a 20g long, except for the much smaller rarer species (and they require very soft water). A 20g is not a lot of room, and as someone mentinoed, gourami can be troublemakers.
Plant the tank at the beginning, and you can add a few fish with no "cycling" worries, and increase the fish slowly from there. The tube you mentioned should be fine, a cool white but that is a nice hue. Tubes need replacing every year roughly, so you can try something different then.