Bettas are quite happy on their own. I know these overbred ones we all like so much (well, most of us before anyone comments
) are quite different from their wild ancestors, but the ancestors live in shallow, slow moving water that is often quite murky - rice paddy-like areas. Males have a territory they defend against all other fish. Females don't have a territory but roam all over. If a female goes into a male's territory, if she's egg heavy they'll mate and then he'll chase her off. If she's not egg ready, he'll chase her off without mating. Males don't have company in the wild. And our bettas have been selectively bred for many many years to be aggressive - don't forget they were domesticated for fighting long before they were kept as pets.
Some will tolerate tank mates but others won't tolerate even a snail - they bite their feelers and harass them to death.
Bettas need a tank of at least 5 American gallons, that's 19 litres. They prefer tanks that aren't too tall as they have to lug those fins up to the surface to breathe. They need a heater, and temps of 76-86
oF, 25-30
oC. The filter flow should be fairly slow so as not to blow the fish around the tank. A filter that looks too strong can be adapted. Decor should be smooth. Real or silk plants rather than plastic, with a tallish broad leaved plant for the betta to rest on just under the surface. A cave of some sort. And things for him to swim though. Some bettas can get bored and start biting their own tails.
They are better fed on betta specific pellets with live/frozen live food as a weekly treat. Bettas are pigs and will stuff themselves to bursting so take care not to overfeed. This is another problem with having tank mates as bettas often eat their own food then the food meant for the other fish as well, particularly if those other fish are slow to feed.
You could try cories, habrosus being the one I'd suggest if you could find them. Small, bland colours and stick to the bottom of the tank out of the betta's main area. With the Aqua Nano having a small footprint for the volume, pandas might be too big, and pygmy and hastatus cories tend to swim mid water a lot. If you do want to try it, put the other fish in first and the betta after, that way the other fish are part of the scenery when the betta goes in rather than a later invader to his territory.
The honey gourami will be fine in your 180 litre - I have a pair in mine. Be warned about girlfriends as I've had more trouble with trios than pairs as the females didn't get on. This species is fine as a pair. Though I had trios in my 125, maybe they'd be OK in a bigger tank. Leave moving the gourami until you are about to put a betta in the tank (or tankmates before the betta if you decide on that) to keep the filter bacteria in good order.