People if you wash your gear when you get home paint will come out 95% of the time.
As for keeping the place clean of it. Your not going to get it all. How ever you will need to have the staff clean it down every night. Next step is drainage. Sure fields wash their indoor fields down. How ever when you use gravel or anything like that it soaks up the water and paint thus resulting in soup. You need to have a drainage system ( possibly a grate) that has a slanted floor under it for water and paint to go somewhere and not be stagnet.
Fans are also key. With everything being damp you need airflow to avoid mould. Iv been playing paintball a long time and thats key when it comes to indoor fields.