You can have 1 dwarf Gourami and up to 10 Kuhlis, make sure your Kuhlis have lots of places to hide if you want to see them. Yes I know that sounds silly but the more places they have to hide the more they come out into the open.
I would suggest a lot of leaf litter like Indian almond left.
I would get some live plants, and yes on the Almond leaf , the IAL will turn your water yellow but thats not a problem the tannins are good for the fish.
Just curious, Why only 1 gourami allowed? Also- if i put a lot of IAL in a small tank like this (10gal) wont the water become dark? A yellow or light tinted coloe wont bother but if it is reddsh
Or black i may not want that.
Dried oak leaves will give plenty of cover as well, but not as much tannin. I use them in my betta tanks and they work great. Just be sure to collect from a clean environment and only the ones that have already fallen, not green leaves.
The dwarf gourami doesn't get along with others of their own species, they aren't schooling fish like tetras and kuhlis and prefer to be alone. If you get more than one they will fight and the dominant one could very well end up killing the other. There just isn't enough room for two aggressive fish to live in harmony. It might be doable in a 29 but even that is iffy.
I agree with Nick, lots of hiding places and preferably live plants. I have 4 kuhlis in a well planted tank. They never shy away from me nor hide away.
This is what I mean by well planted:
Also, you will need a smooth substrate, like smooth pebbles or sand. Sharp substrate like your average colored rocks are too rough on loaches
You don't have to have live plants, but they are greatly appreciated by the fish. It all comes down to ground cover for the loaches. I think if you add a few plastic plants towards the corners and back of the tank, then maybe a medium sized hollow decoration, like a log or piece of driftwood, and finally a hand full of oak leaves will be enough cover.