I try to stay out of the cater side,as it is too much work when you don't do it often.
When forced,many of us have used Elizabeth as a bbq guide as she does q as a living.
From our FIND tab above a search gives me her response.
Elizabeth's cater PortionsIf mostly adults,I'm thinking 1/4 lb cooked/lean brisket should get you there.
If you figure 50% loss on packers,that should be about 75 lbs for 150 1/4 lb portions.
In the South the crowd may lean towards the pork and the SW towards the brisket.I like to cook one extra packer to be sure and it is always welcome in doggy bags.
If you have kids there,they often fill up on all the assorted junk and some hotdogs are always a good fallback.
My teammate,Ribdog ,does many more caters and he may chime in directly-altho he is involved in one right now.
Hope this helps a little.