As you have read already, the selected fish are not suitable for a 10 gallon tank. The bio-load alone will be greater than a suitable filter (tank wise) can handle. The Pleco alone needs a tank of 4' or greater length. the Mollies will need a 20 for each pair. I would suggest you either return all the fish or buy a 55 gallon tank and switch over everything - water, media, filter to it. Since you will now be trying to finish your cycle with fish, you will need to do a daily w/c. Your ammonia will start to spike risking the life of the fish. You will need to change as much water as needed to reduce ammonia as close to 0 as possible. Ammonia, is the base upon which the cycle is started but too much can burn and kill the fish.
I have a Hypostomus Plecostomus and will tell you that they indeed generate a great deal of waste. Although initially an "algae eater", they will need more than algae to sustain them and they eat less algae and become more omnivorous. That is their natural habit. They may continue to eat algae but it will be in smaller amounts.
Keeping golldfish isn't the same as tropicals with the exception of the need for clean water. The Pleco does not have the same water requirements as the mollies and for that reason they are not compatible.
For the future, I would suggest that you ask your partner to not buy fish with out first checking with you. There also needs to be only 1 (one) person making all the decisions about the tank to help eliminate problems. If you wish for joint care, you should have the final decision. My wife helps me with the fish care and takes over while I am in the hospital (about 3X a year) but makes no changes unless she checks with me first (providing I am in a position to make such decisions). When I am not able to tell her what needs to be done, she has another experienced person come in and take over. At no time do they ever add fish.
Good Luck!!!
