The lotsa pasta spaghetti page has basically all I know about reheating pasta.
If the spaghetti/sauce do not have meat, this is not enough picnic shoulder for everyone (assuming bone in). You would need 60 pounds to have plenty for everyone.
If you don't want to make that much roast, you might consider a pork-based chili, or pulled pork for sandwiches.
You basically want food on the serving table for less than 2 hours; 1 is even better. Hot food needs to stay above 145. There are food safety articles that will help you on this site.
See the safely reheating turkey article in the holiday cooking section at the top of big pots for how to reheat sliced meats.
