Is this a business or a social enterprise to fulfill your fantasy. Best to decide that up front and set your set a target and an absolute maximum budget in advance, so you can track against it. No cheating, either, eg by buying supplies from your usual housekeeping account.
I'd start with a lot or research and desk work (sorry)
Firstly, by setting up a new account, easy enough to do on line. May have to be converted to a business account in due course but I'd give myself a few gos before deciding whether it was going to continue. Say three months ?
Then I'd plot out who the customer is, maybe identify key groups of people who want to attract
I'd also work out the 'customer journey', which may need to be different for different types of customers.
Next step is to plan out what you will offer those customers. Signage to make them aware that you exist, show where / how to order, where to collect etc Even a few customers will get in each other's way so it's good to plot out the flow through your stall.
The kind of customer will be helpful when you work out what payment systems will be appropriate and expected : cash is easy but costly to process and needs change/float to run smoothly. Tech savvy customers may have a strong preference for swiping card/phone which requires relatively simple infrastructure these days. Costs / support another area to research.
Which takes us back to your record keeping. What records do you plan to keep. Cash means a manual record , swiping means you know the vale of each transaction automatically.
Then consider what if anything you can upsell. Biscuits, other snacks etc all to get factored into the journey depending on the type of customers you want to target.
And who will be 'serving'. Do you plan to do it all your self. Company might be fun but adds complexity. If you can find someone who would be happy to lend a hand from the start it would I think be good. To set up/ break down. And mind the stall while you have a comfort break.
Lots of decisions required. Don't stress about them, but I would encourage you to keep a journal about these things and not hesitate to adjust as reality unfolds.
Enjoy.