this is a neat story! I have wanted to add some cories to my 29 because so many people here are fans! Look for a thread called Crazy Cories Anonymous, i think in the aquaria off-topic forum. super funny read!
By the way, since you added them already make sure you test your water parameters more often than usual, maybe even daily for the next week then twice weekly. Any ammonia or nitrites above 0.0ppm will be a tip-off if the filter's bacteria colonies are "over-fed"
The best advice I can give to help you avoid a mini-cycle due to the jump in bio-load is feed less! put everyone on a diet and don't spoil the cories with food yet. let your bacteria colony catch up as slowly as possible (water changes should do the trick no big deal)
plus they probably can snack on whatever the pleco doesn't fancy.
I'm going shopping me thinks