On 54 a store is a site that declares what it sells: the prices come from the site, the payment goes to your own Stripe account, and an order counts as paid only when Stripe says so.
A store is not a page with a Buy button. It is a list of products with prices nobody else can change, a checkout, and an order that only exists once the money arrived. Most quick stores get the last part wrong: they mark the order done when the customer comes back to the thank-you page, which anyone can open by hand.
Where this gets hard on other tools
A generated store often ships with a Buy button that writes the order straight to a database, or a success page that marks it paid. Both can be triggered without paying.
On 54 the products are read from the site when you publish, the checkout is Stripe on your account, and the order turns paid when Stripe confirms it.
Paste this and change the products
a store for my handmade candles, three scents at 18 dollars each, with a cart and card payment
Every change is a sentence: "add a fourth scent", "show the price under each photo", "add a gift wrap option for 3 dollars". Publish again and the catalog follows the site.
To your own Stripe account, which you connect in the payments tab of the site.
No. The price comes from the products the site declares when you publish, and the server checks it.
When Stripe confirms the payment. A visitor opening the thank-you page by hand does not make an order paid.
Yes, if you turn it on and your Stripe account has crypto enabled; it is USDC, for prices in dollars. Without it, the checkout takes cards.
No. The site declares what it sells and publishing loads it. You change products by asking for the change.
You can download the files and the data whenever you want.