They can co-exist just fine but ideally you need a sand or very fine (2-4mm) gravel base with no sharp edges otherwise you may have issues with them wearing down their barbels as they sift through it all. Some people get away with gravel, your results may vary.
I wouldn’t do neons and cardinals personally as they are very similar. One or the other is fine, neons tend to be a bit more robust out of the two but I prefer the look of cardinals. What about a centre piece fish like a pearl gourami or two?
I would do 2 species of mid/top water fish max and something for the bottom.
15 Neons or cardinals
2 peal gourami
6-8 of the smaller Cory species like Pandas
You could add some shrimp and a few nerite snails to finish things off. Nerite snails won’t breed but may lay eggs which are white dots.
I would avoid Brisslenose Pleco’s - overrated, nocturnal so hide all day, they need a special diet and will eat your pants. I would actually avoid all Pleco species.