If I had to guess, that'd be a platy of some sort, which seems to be a pretty easy going fish that isn't going to cause problems. I didn't read the list of what you have, so some fish may have problems with him, but unless they're aggressive breeds, they should probably be fine.
Welcome by the way. I'm pretty new myself, and everyone here is super helpful.
EDIT:
Oh yeah, guppies and mollies and a pleco should be fine together. I don't know anything about CAE though, except that they get big.
The only advice I have to give is be careful with livebearers (which guppies, mollies, and platies all are), as they breed fast and you could quickly become overstocked.