The basic business model does not need to be very different from other existing ones you could learn from. Just make sure you know the region and people (your customers) in that region. An architectural design firm could always be full of possibilites, so you don't need to worry about the business model and such things related to a small city. Just try to figure out your core value, learn the customers and distribution channels, gather the resources you could have and move forward. You would be all good!