20 years ago some friends and I bought a pizzeria. Not cupcakes, but similar in that we had 1 item on the menu. It took a while to turn it around, but we did.
1 This used to be standard advice: don't expect to make a profit for 1 1/2 years. You could, maybe you will, but don't count on the business paying your personal bills for 1 1/2 years. You'll have times when you sell lots and can't keep up with demand, and there will be times when you can't afford to buy flour. Any money you make should be used for supplies, equipment, a nest egg for when the water main gets shut off. If you do spend $30,000 to open your doors, it could easily take 1 1/2 years to make $30,000 of profit. If you are and instant hit--Great!!! Just don't expect it.
2 Are you talking about a mid sized city or larger? You need a lot of potential customers for this to take off. Are there any established businesses that will compete with you? You'll have to offer something other places don't offer. High quality, nearby location, etc. It'll be difficult to compete with a popular cupcake shop or even bakery.
3 I assume you will provide most of the labor yourself. That will cut down costs. Buy used equipment and replace it with new later.
4 Be flexible. If your favorite mango and rosemary cupcake sits there but customers keep buying vanilla with pink sprinkles, you might consider making more vanilla cupcakes. Don't take it personally. Your goal is to stay in business so that you can offer up the Best Cupcakes Ever.
5 Start small and grow. Bills will be a constant headache while your sales are growing. Smaller bills mean fewer headaches. Choose a location that can start small but expand. You don't want move location because you'll lose some customers. Two main reasons businesses don't succeed: they expand too fast (lots of bills and expenses) and changing location (lose clients).