if you buy paintballs there and have left over paint can you save it for another day? how fast do you go trough paint? How many people are there on an average day?

Yes u can save them and use them

You can't bring your own paint if I remember correctly. So you can NOT take it home and reuse it on another day. If you are a conservative shooter the stock 200 balls will last you 2 hours. If you are imbued with the spirit of Rambo you'll need several hundred every hour. You can always just buy more between games. On an average day there can easily be 50 to 80 people playing on various fields. I recommend you bring more than 10 ppl and get the group reservation privileges.

We each went through a box of pain in about 4 hours. As for amount of people when I went there were about 40 people, 20 a team.

As long as you bought the paint from that field it should be fine. You will still have to pay the entry fee though. Usually a good attendance