I appreciate that, and your questions really help me improve my writing - I should have included that info!

Crowds: Yes! I was there over what you'd consider a low period for tourists, as well as a high one for Italian tourists visiting from other cities. In both cases from 1-3pm and 6-9pm, you kind of need to hover for a table. Don't be afraid to ask if you can take empty seats at a larger table, it's normal and common to share the long 6+ tops. If one person can sit and the other can go get food, that's helpful, but then the person sitting doesn't get to browse the stalls. Additionally, during high traffic periods, I've also seen some crowd control limiting people getting on the escalators up so that the escalator isn't pushing people into a crowd backed up from the entry way.

Credit: I think all stalls take credit. I didn't try everywhere, because when I was buying a coffee for a euro, I was using change.

Remember that your drinks come from stalls too. If you sit on the side with the (beer) bar, same side as the butcher, the hamburgers, fish, etc, you'll see servers going around. You can order water and beer from them, and you pay them directly. If you want wine, there's a wine stall. Pick a bottle (or ask for help), they'll cork it and give you glasses. Or you can buy by the glass.

I love the market. I have a 3 year old and she doesn't always want to wait until 7 for dinner. This is one place to get some real food, not tourist crap, in the restaurant off-hours.