Not much I can add to the above. :) The mollies can and should pig out on veggies, as you probably know. If they get woozy, a little salt doesn't hurt. They also sometimes don't do well with the crowding we get away with while keeping other livebearers. Doesn't sound like an issue in your aquarium.

Neons and cardinals are mostly carnivores. They will eat most standard offerings so you don't have to start raising fruitflies. ;)

Neons do come from about a 1000 miles upstream from the cardinals. Their waters tend to be "whitewaters" which have a little mineral and fairly neutral chemistry (in case you want to breed them.) They prefer water in the low 70s and may need more food at higher temps.

Cardinals (when they can be found anymore) come from much warmer (80 ish) waters which tend to be those notorious black waters of the Rio Negro system. They actually make pretty good companions for discus (so long as they aren't bite sized.)

We adopted a cardinal which was 6 + years old when we got it (and the 55 that came along with it). It lived a couple more years after that!

I probably should have gotten it a half dozen cardinal companions. At the time cardinals were coming in with really nasty diseases. I didn't want to set up a quarantine tank for them.

Your tank temp, like all community tanks, will be a compromise. You probably already are doing this. As you inch down from 80 degrees F. to the middle 70s watch the cardinals and mollies. Black mollies are about the touchiest of commercial livebearers.

Even when I raised enough mollies to swap for fishfood at a local shop, if the mollies' temperature dropped too low, they got pretty little white spots all over their previously spotless bodies. :(