Hi Gilkins,
Resa has just about covered everything I would have said.
She refered to cycling - depending on how you did that you may be fine or you may have problems coming. Shops and tank manufactureres very rarely tell you anything useful about cycling. This is the process of growing bacteria in the filter which remove toxins from the tank. One species uses the ammonia secreted by the fish as food, and turns it into nitrite, the second species uses that nitrite as food and turns it into nitrate. It takes several weeks to grow these bacteria in sufficient numbers to keep both ammonia and nitrite in the water at zero.
Most shops won't tell you about this, or they'll tell you to add bottle bacteria. But the majority of these bottles don't work.
If you just let the tank run, then got the first fish, it is quite possible that you had ammonia and nitrite in the tank for a few weeks. It has been a few weeks since then, so you may have enough bacteria by now. But if there was either of the two toxins in the tank at the beginning, the fish could have been affected and be more likely to become sick.
Resa mentioned the number and type of fish you have, and I agree. Apart from the gouramis, you have several shoaling species in numbers that are too small. Shoaling fish are those that live in groups of hundreds, if not thousands, in the wild. When there aren't enough of them, their instincts tell them that the rest of the shoal must have been eaten so they are constantly looking out for the predator. This is very stressful, and stressed fish get sick very easily. It is reckoned that fish lose count around six, and any number at or over six is regarded as a shoal. So to be 'happy', you need 6+ red phantoms, 6+ black phantoms and 6+ of each of the three cory species. Yes, you need 18 cories if you want three species.
I've looked at your post in this thread, and the one in Resa's thread about her gourami, and I can find anything about your tank size (though of course it does take me a couple of hours to wake up properly in a morning and I might not be seeing what is written there

)
Both
black phantoms and
red phantoms need a minimum of 70 litres and a length of at least 60cm. You'll see in those links that at least six each are remommended, with at least 10 of each being better.
Cories need a tank with a biggish footprint - that is a long rectangular tank rather than a cube shaped one.
I wouldn't worry about any fry from the gouramis - the chances are the tetras would eat any eggs before they hatched, and certainly any fry once they got big enough to swim on their own. The biggest risk is the male gourami attacking the female if he wants to breed and she doesn't.
Can I ask a silly question? You definitely have a male and female gourami? Some shop workers don't know the difference. If both your fish are red, you have 2 males. Female dwarfs are silver with a hint of colour.