I can't speak to laws, regs, and all that, but I can tell you what I do for larger servings. I do fundraising cooks at my kids' school, teacher lunches, etc. I pre-cook the weekend before (this is pulled pork btw), get it cooled, vac-sealed and frozen, and boil in the bag on site. I'll do lots of 3# bags, then I'll have a couple 2# & 1# bags for towards the end of the event. This works really well for me.
If I were selling commercially, I think I'd want to cook fresh, but I can't say for sure without being in that situation. I do know that a big draw for selling BBQ is a smoker puffing out delicious smelling smoke - I cook MOINKs on site to get that smell in the air, and it does seem to draw 'em in.