I was having trouble with this too. If It's with your browser or something, I can't help much, but I did notice that the only things I can put in the cauldron are noodles and the ingredients for vegetable soup.
As for the plate, it's very order-dependent. You have to put the noodles on first, then meatballs, then, sauce. If you put the sauce on first, you aren't able to put on the meatballs.
I do agree with you though, being able to review the customer's order would be nice.