20 pork shoulders, short; how much depends on the weight and if bone in, and whether you are going for roast pork or pulled pork sandwiches.
This is a calculation; you only get a bit less than 1/2 pound ready to serve pulled pork from each pound of bone in raw shoulder. How much you cook depends on whether it is served plated or on buns.
1 pound ready to serve per 3 is the amount needed for plated, so for 350 people that is about 240 pounds raw bone in
1 pound per 5 for sandwiches, sauced and ready to serve, which is about 150 pounds raw bone in.
Add
pickles, sliced, 1 gallon per 100
onions, 8 pounds per 100
table sauce, 1 pint per 10
rolls- 5 per pound or 12 sliders per pound. Sliders are better for this type party, neater to eat and less waste.
If served plated, 12 pounds bread/rolls and 2-3 pounds butter per 100

24 lbs. of hash browns for cheesy potatoes in the roaster, .
one roaster feeds about 60. Remember that each roaster requires its own electrical circuit; two roasters will blow any single circuit.
Here is the recipe I use (scroll down to the bottom of the page), and I START with 20 pounds potatoes per 100, defrosted overnight in the fridge and drained before cooking
ellenskitchen.com/bigpots/plan/bfast100.html

8 gallons of baked beans
I plan 3 gallons (4 #10 cans) per 100. For 350, 11 gallons or 14 #10 cans

24 lbs. of coleslaw.
I plan 2 1/2 gallons per 100 minimum, which starts with about 24 pounds of raw whole cabbage per 100, plus add-ins

This is a very light menu for a wedding reception dinner, please consider adding an appetizer plan and here is why:

A self-catered buffet is a real challenge to the organizers, and things don't always come together as smoothly as hoped. By planning and setting up an appetizer area or "nibble table" which is ready when the guests begin to arrive, the cooks and servers have time to complete the arrangement of the dinner buffet. This is especially critical if there are children among the guests, or there is a wait before dinner, as at a wedding reception.

This does not have to be complicated. Three items, plus a punch (8 gallons per 100), or two if one is alcoholic, are sufficient. Typically, include a fruit tray (see the fruit tray page), a cheese tray (per 100, 8-10 pounds cheese, some can be logs or spreads, and 6 pounds crackers) and an attractive dip or spread (per 100, 1 gallon dip/spread/salsa or 2 gallons queso and 6 pounds potato chips or 8 pounds corn chips) ; or you can go with a dinner theme such as TexMex with chips, salsas, Texas caviar and guacamole; Italian with bruschetta or antipasto; maybe shrimps or other cold seafood, if budget permits.

One appetizer service area serves about 100 guests, you would plan 3.

Finally, be aware that a party this size definitely requires a day-of staff that will NOT be at the wedding: 4-5 in the kitchen and 15-18 out front to set up, serve, and clean up the party. At least 4 serving lines, and 6 would be better.