Here is some advice for what it's worth, just my humble opinions.
1. Get a Greenville city license if you are working in the city limits. Get insurance and an applicators license if yo are going to offer weed spraying and fert. applications.
2. Mower? Do you want to walk or ride? Gets pretty hot in my area and I prefer to ride. I would say about a 48 inch or bigger. What dealers are close by and how are there service and parts departments. Check out craig's list also for used equipment.
3. Word of mouth is always the best and cost effective. Ask your clients for referrals. I advertise in the small community papers.