I replied to your other post, so I may as well give this one a go also.
1. What size groups: Well, this is a question you have to answer for yourself. Consider your abilities, your experience, your equipment, and your time. If you plan on doing this part time, take that into consideration. If you plan on feeding larger sized groups, can you hire staff or enlist friends/family members to help? I would think over these issues and try to come up with a number you are comfortable with. An important thing to note also is that when building your reputation, don't bite off more than you can chew. IMHO, a catering business is best built with positive word of mouth, and the business wrecked just as quickly by negative. Don't take on more than you can handle, or your quality and service will suffer. For example, with the equipment I currently use, I can cater jobs up to about 500 people, serving each guest 2 types of meat, 2 side orders, and the related fixins'. I will not even bid a job with that menu if it is larger than 500 people, because I know we can't do a good job, given our equipment and staff limitations. Knowing your limits is helpful, and when you can push them. This weekend, for instance, we are partially catering a job for 850 people, but we are just providing the brisket. The event hosts are handling the sides, drinks, and service. While I won't do our standard catering menu for a group that size, by providing just the meat, I know we can handle it with capacity to spare.
2. Commercial Smokers to handle the job: There are quite a few commercial smoker manufacturers out there. Again, you have to look at the size of groups that you will be feeding. As this is a Cookshack website, and I use their Model 350, I suggest you peruse their site first. Also, you will find a call to their offices a helpful experience. They are friendly, knowledgeable, and the posts on this forum are trully indicative of the level of customer service you can expect to recieve from Cookshack. With that said, do your homework, other commercial smoker manufacturers include but are not limited to: Southern Pride, Ole' Hickory, Klose, Traeger, and Alto-Shaam. A couple of notes on these, Cookshack also represents Ole' Hickory, so I assume your call to Cookshack can cover this also. If you are considering a BBQ operation only, I would tend to discount the Alto-shaam, as this smoker-oven appears to me to be greared more towards a full line restaurant, and while they make good equipment, Alto-shaams are pretty high dollar. Check 'em out anyway for the sake of being thorough. Also, make sure any smoker you consider is NSF certified. Many health departments will require that. Speaking of which...
3. Permits and licenses: This is yet another area you'll have to do some homework in, as regulations vary from state to state, to county, to city. My first call would be to whatever Health department has jusitiction over the area in which you wish to serve food. This can be either a county, parish, city, or otherwise depending on where you live. If you wish to serve food in multiple areas of jurisdiction, call them all. Get the numbers from the phone book. You may get directed to different numbers a couple of times, but eventually, you'll get the right people. Once you get the right people, explain what sort of business you are wishing to start, and ask them to mail you a copy of any current regulation guides that apply to your business. Also, if you are dealing with a city or county office, ask them if there are any further state regulations you need to be aware of. If you are dealing with a city or county agency, I'd call the state to be sure, regardless of what your local office says. Sometimes these bureaucracies aren't always on the same page, but if you do the homework, you are covered.
Once you've coved the health regs, yet another call to the local government is in order. You should find out if a business or vendor license is required, and the steps involved to obtain a sales tax ID number. Unlike the Health dept. regs, the local people should have a pretty good idea of any additional state permits or forms you may need to fill out. In my experience, they seem to have the way you pay taxes a lot more ironed out between agencies than how you serve safe food. Hmmmmmm....
Along these same lines, it's not a bad idea at all to consult a qualified attorney. A lawyer versed in these matters may at least save you some paperwork, and may at most save your financial butt! Along with the permit stuff a qualified lawyer can help you with selecting the proper insurance for this venture, and there may be some liability benefits if you were to incoprorate or become an LLC. On liability, don't even think of trying this without some sort of insurance! You can do everything right, serve safe food, comply with all regulations, and someone could still sue you. Insurance covers your A**! Also, having an attorney set this deal up for you provides a little protection, because if you are clear and upfront with your lawyer about what you want he/she to do, and what you are going to do, and somehow a judgement is made against you, there's a good chance you may have a malpractice claim against your lawyer. Assuming, of course, you followed the regs, had the permits, etc. I'm sorry I'm in such a litigious state of mind, but I like better safe than sorry, and there are fat people suing McD's, BK, and others right now for food that was probably served within all of these guidelines. ARGGGGGGGHHH!!!