Thank you @Essjay . So we have soft water, somewhere around 4 to 6 dH. That's all we need to know on that front. And the dimensions tell us that issue. So, I wold say from the original list in post #1 here... rehome the mollies, as you intend, they are not going to make it. The other listed fish are fine in soft water. To the numbers. Tetras and cories are shoaling species, so there must be a group of them. Everyone want numbers, how many in this tank, etc, but the more important aspect is having enough of each species to not cause stress, so the fish are healthy. Most species are better with ten than five or six, there is now scientific evidence for this. The nature of the species also factors in...a more aggressive species needs mor of its own to control the aggression. But numbers really do matter, pre-eminently. If you cannot have a decent number of "x" species, then don't have that species because it is not going to do well long-term.
The cories must have 10-12. Same species or different species here does not matter--one of the very few cases this holds true. So increase the cories to 10, 11, 12, even up to 15 will not hurt anything, and more to the point, the cories will without any question be healthier and less stressed. If this were my tank, I would have 12-15, no fewer.
To the tetras. The Bleeding Hearts are peaceful but a tad feisty, and numbers have a lot to do with this. I would up these to 10 or 11. This should avoid fin nipping, which they can get into without enough of them. The cardinals, I would up these to 11 or 12. This is an interesting tetra; observations in the habitat by one explorer showed that the cardinals were in a general gourp of several hundred in an area. But within this area, they divided up. Where there were branches and chunks of wood in the water, the cardinals remained in groups of six around these. But where there were no such branches, but floating plants, they were in huge groups. The groups of six also joined together with all of them at the first indication of a possible threat. From this, I wold say the 10-12 is more likely to keep them settled, which means less stress which means better health.
The single plec is fine (hope it is a small species?) provided there is one good chunk of wood for grazing.
