I came here to post what mowerbrad did. Spend a few hundred dollars NOW for an attorney's and accountant's opinion. Each time I have started a business I have asked both what the best format is.
If your choice is sole or LLC then IMO LLC is BY FAR the best way to go.
I would ask an account and an attorney if you should go sole-proprietorship, LLC or S-Corp. If you choose one of the latter treat it like a business that is seperate from your personal stuff. The most important is that it has its own bank account.
You must have a hell of an operation if you need a F350 crew cab to pull your mowers around. Whatever you buy, buy it with cash. Debt stinks. A business with little or no debt has a HUGE advantage over a highly levered business. I fail to see how an F350 crew cab will grow a mowing business unless you are strapping a 84" mowing deck under it.