That would mean each individual wire is 12ga.
As for banana plugs, I prefer them. The first time you have to disconnect and reconnect your speakers you will appreciate having taken the time to add them, especially on the reciever end.
I haven't used the ones from monoprice, so I can't comment. I have used the ones from BJC and they work fine. My banana plugs are a mix of BJC and the ones from
Parts express, part number 091-330. Both are good quality. (I don't use the locking ones, I like to heat shrink over most of the connector. That doesn't mean I think they are bad, lots of people like them and highly recommend locking banana plugs.)
Jack