Well I don't think GFO and filter floss would be much of use for such a small system. Carbon would be an important thing since softies like to do funny things in the water and carbon is really helpful to suck those out.
For my 20 gallon, I use a HOB skimmer, 2 aqueon 20 filters (one filled with LR rubbles + carbon + phospad and the other one has two chemi-pure elite and I will be adding purigen at the end of this month) and till now, I have not done any WC for the last two months other than top-off and dilution of salinity. On 8th, when I left the country for vacation, my nitrate was undetectable (was running for more than a month) and hopefully after coming back to Calgary, I am expecting to see very small (maybe 5ppm) or undetectable nitrate. If undetectable, they I will consider my filtration to be perfect for my tank
