What a rush it must be to see a gallery with work you live so much wanting to sell your stuff. If you are going to be producing for them, you will have to learn how to pace yourself, so that you can keep working with less wear and tear on the potter. Sometimes, the best thing you can say as an artist is "no".
I bet that your stuff will sell very well, and for very nice prices!
If the items in question are small, them a multiple mold works just fine. We do sake cups this way, and tiny vases. For anything bigger than a teacup, double molds may work, but more single molds work better than gang molds. When there is enough plaster to pull the right amount of moisture, they get heavy quickly. Add the weight of the slip, and dumping them is a two person job. Also, the slip you dump tends to go everywhere, sometimes into other molds in the gang....
You might consider using a different height work surface. Either use chocks to raise the table you have now or change your chair height. Perhaps sitting on a balance ball, even. If you have a variety of heights available, you can move around as you work. If you work standing already, get some good floor mats.