Like you're doing you have to figure timing.
When are you serving them, when will you reheat them and when will you have time to pull?
Smoke them ahead is probably safest if you haven't done it. I would do them two nights before so they're only in the fridge the previous day.
35#, could be 4 good sized butts or 6 smaller ones and you could do all of those if you squeeze them in (they'll shrink) a little.
Quantity: 35 lbs will be about 17.5 after cooking (average) or 280 oz. Divided by 50 is 5.6 oz per serving. A good sized sandwich.
If you're worried, just do a them up the day or two before. Take them out, wrap in plastic wrap and then foil -- don't pull them yet.
When you reheat, you want them to get to pulling/serving temp but you don't want to cook them more so just reheat. 200 for 2 hours is more than enough. If you use good quality plastic wrap it won't be harmed in the reheating. If you don't it will disintegrate. If you're worried, just take the plastic wrap off before reheating.
Pull after reheating and add sauce and don't forget to add a little more rub when you pull.
You can also reheat them but don't pull them all (hey if you want to impress them, let them see you pull them, sauce them, rub them). Just reheat all of them and put them in an ice chest for holding as needed.
Russ