Well first things first: we need to know how hard your local water is. All of the fish you are describing are soft water fish and won't show their best colors or live very long in hard water. You can often find your local water hardness online as many cities publish a local water quality report. Look for the GH, KH (carbonate hardness), and pH.
Unlike some barbs, ruby barbs are rather peaceful (if a little active) as long as they are kept in large groups (more than 7 individuals). They go well with other barbs, rasbora, loaches, and corydoras. Depending on the species of pleco, it could be a bad idea. The common pleco will get large enough to make a meal out of smaller fish (and it usually will try; they love sneaking up on little fish at night). Bristlenose pleco would be a much better idea. You have enough room for a male and two females and might even get them to breed.