This means that you have 10 gallons so you can have 10" of adult fish.
The tetras can count as 1" each, the danios 2" each, the gouramis 2" each and small catfish say 3" each (depends on species).
As you can see for what you suggest you're looking at 23" of adult fish, twice the capacity of your tank
Try and decide what kind of tank you want, ie. community (lots of fish) or species (few bigger fish) and work it out from there