Niche specific site would do for targeted audience. But if for financial constraint you can begin with one that entails all cities.With hyper links for all cities. Online business is most about the marketing and traffic thing.
Many locksmiths, plumbers etc nowadays dont even have a website. They create a free business page with Facebook and stay 'social'. Its a great way to do business, to bring in new customers and look 'friendly'. Websites are so static and so i would recommend a business facebook page as your face to the world. You can then promote this directly in the search engines.
content and keyword research
After Google panda and Google penguin update, no one can say that best method in SEO. According to me, You should create user friendly sites where users spent their valuable time.
Only doing infographic, article submission, guest blogging and blog posting, your purpose is not going to be served. You must use SMO techniques with SEO because it plays major role in SEO.
I am a locksmith and I want to start developing websites for my business. What is better, sites for multiple cities (locksmithofnewyork.com and more cities) or one site for all the cities with the business name (____locksmith.com)? Thank you.