As it's a stag just accept it will be a money pit. Estimate to he budget of the group, buy paint in the most cost effective batches, the probable best price is likely to be for 1000. If so have every 2 players buy 1000 between them, then the people who are firing the most paint should next buy 1000 in twos again
Just do the drinking after the paintball
Forget paint grenades, smoke & flashbangs. Just spend on paint
Try some tactics in each game if you wish but it will all change as soon as people run forward.
Have the stag events been planned or is it early days?
I would say go for a half day of paintball, then something else, then drinking and the other activities that go with that