A regular wants to pay 500 up front and eat through it over the month. Should I use a gift card, store credit or a house account?

Store credit, if they will only spend it at the counter. Open Marketing → Store credit, type their phone number and 500 in Add credit, write why, and it sits against their name; the cashier picks Store credit on the Charge screen and types their number. A gift card if they also want to spend it on your ordering page, because a gift card code works there and store credit does not. A house account is the opposite idea: they eat first and pay later, with a limit you set. All three are money you hold, and each page shows the total you owe at the top.