A half pound finished product per person would be way over buying. Don't forget that there are people who might have one sandwich and not even finish it while there will be others who will have two and finish both. That is why I like the Hawaiian rolls as sliders. It allows people to portion out what they want better. And the ice cream scooper will allow them to ball up a measured portion for each sandwich that is predictable. Plus it is fun.
Four sliders could equal one full size sandwich. There will be some that only make two sliders and others might have six or eight. And then add cole slaw on top for filler.
Also serve some baked beans. A pot of beans is easy to make and will add that filler you need.
Costco sells those large packages of Hawaiian rolls and you can buy the beans and slaw pre-made or make your own. There are some recipes for Wasabi slaw that are just fantastic and of course there are people on here who can give you a great baked bean recipe.
I would let people sauce the sliders themselves. You can make up a batch of Hubbard Bubba BBQ sauce that is made with Dr.Pepper and I believe Dee has posted that recipe somewhere in this forum. That sauce is really good and people will be amazed when you tell them it is made with Dr.Pepper
The best thing is to have the pulled pork be prepared in advance that way everything is covered and people don't go away hungry.