well, lets talk about business for a minute. since you are asking about equipment I will assume that you are already set up to get your business license, fictitious name registered, liability and equipment insurance, and tax ID.
once you decide on a camera, you need to get TWO of them. you cant realistically set up a business with ONE camera, ONE lens, and PRAY that nothing goes wrong. you will also need studio lighting. we do mostly weddings, and not a lot of studio work. when we DO use a studio, we rent space from a local photo shop and bring our own equipment. you will need several flashes, stands, and diffusers/umbrellas. backdrops in multiple colors, props, stools or chairs. several different types of lenses in different focal lengths. you could go with several fixed focal lenses, or a zoom or two...preferably both. a GOOD tripod and head. radio triggers if you need them. backups of your lenses. an extra extra flash or two as a backup and/or additional lighting. the list for studio equipment is as long as a wedding photographer. not only do you have to be prepared equipment/knowledge wise to shoot 1 person, or 2 people, or any number of people, but you also have to be prepared for any piece of your equipment to quit working at any given time. AND be able to grab your backup and get back to work within minutes. hopefully this is all stuff you are prepared for BEFORE you start taking clients.