Gourami males are territorial. This means they are defending the nest area. They do not harrass the females to make them breed. They are chasing the egg-and-fry predators out of their territory.
Basic life style:
Males build nest, defend the area.
Female ready to breed
comes into the territory. If she is not ready he chases her away.
He chases her off and tends the nest, eggs, fry.
If she stayed in the area she might eat eggs or fry.
A 55 gallon tank with LOTS of tall plants might be enough to keep the females out of sight. The male might just claim part of the tank. Maybe.
Some Gouramis are milder than others.
Dwarf Gouramis, Paradise Fish, Betta splendens and Three Spot Gouramis (all color morphs) are about the most aggressive. General recommendation is one one of these per tank.
Moonlights and Honey Gouramis are probably middle-level. I have had them work in pairs or trios, and had some aggression. Some of this may have been tank size, or lack of territory markers.
Pearls and Snakeskins are usually among the milder Gouramis. Snakeskins get too big for a 55, but I had a trio in a 125 (6' long) several years ago. A couple of Pearls would highly likely work in a 55 (I have kept them in a 3' long tank)
Gouramis are individual fish, with their own personality. I have heard of Dwarf Gouramis so aggressive they had to be removed from the community tank because they were attacking all the other fish, even those that swam lower down. I have heard of one person with aggressive Pearl Gouramis.
If you can get all females (any species) they are more likely to get along, same way as a group of Betta females are usually OK together.
Milder fish like Otos, mild schooling fish, snails.
then pushier fish like Rams, Gouramis.
Substitute for Tiger Barbs: Pentazona Barbs (5 banded barbs) or Ruby Barbs. These can be a bit pushy, but nowhere near as aggressive as Tiger Barbs.
Cherries are nice looking, but not exactly schooling. The males are a bit too feisty to get along like schooling fish. Checker barbs might work.
What if both nitrite and nitrates are really high but ammonia is low
The bacteria that convert ammonia to nitrite grow fast, so ammonia will start dropping first. You need to keep adding it. Return it to 3 ppm once a day.
The bacteria that convert nitrite to nitrate (Nitrospira sp) are slower growing, and they don't even get started until after the first group has started generating nitrite.
Once they do get going the nitrate starts rising, but the bacteria are not up to dealing with all the nitrite right away, and the ammonia --> nitrite bacteria keep on producing nitrite.
... means the fishless cycle is roughly 1/2 to 2/3 done.
Also, as noted above, not all nitrate tests will read right when nitrite is present. Ignore nitrate and concentrate at keeping ammonia and nitrite in the right levels to grow the bacteria as fast as possible.