Hi, I might be able to give you some info.
In early 2010 I started a catering company in Northern, VA. There has been a steep learning curve but it's going very well. I may have a different perspective than some of other people you get responses from or speak with and I'm happy to answer any questions you might have...just too much to type right now and nobody wants to read through all that!
But in short, I started with a WSM 22" and quickly picked up a pretty good size trailer mounted 4860 smoker from Heartland Cookers in Sikeston, MO. If I've got a big event I use the 4860, if I need less I'll use the WSM. I rent a commercial kitchen from a local church so I'm legal (licensed, insured, etc.) as far as other equipment, I had almost none, but would buy things as I could, here and there. Usually at Restaurant Depot.
Let me know if I can help.