I HIGHLY recommend you read every post in the Pro's forum. You won't find a better one-stop-shop for Professional Q information. There's a lot of great questions here that cover just what your asking. And many of the issues you face.
Think about target audience and the work involved for whatever you're planning on smoking/serving.
Jack is a good resource (aren't you Jack) and they've recently started a similar business and the details are here.
Sauce. Well it depends. If you don't already have a sauce you can certainly make a sauce, if that's what you're wanting to market. But look at the costs involved. Are you planning on reselling it, then you get into the whole co-packing issue for bottling.
For BBQ, look at your competitors. I see a LOT of crap sold as BBQ that I wouldn't feed to a dog, let alone my family. But it's the nature of the beast, hard to turn out good Q in quantity.
For smokers, think about your business plan and volume. Just having a big smoker doesn't guarantee success. You have to think prep time, cooking time, hold time. Do all meats need the same temp or different temps. Lots of variables.
And last but not least. Don't take this wrong. I hear/see a LOT of people that think they can open a Q business that all they've ever done is in their backyard. You're doing the right thing, you're asking questions. They don't even cater. I would suggest catering small jobs to get your recipes refined and your experience. From a business perspective, opening up a business that you're only vaguely experienced at is a lot of work. Not that it can't happen, but it's a lot of work.