Yes. HPA(High Pressure Air) tanks can be refilled. Sorry, Co2 is not available at this time.
Like all other action sports (football, basketball, etc.) paintball is safe as long as adequate protection (a mask) is worn and safety rules are followed. A 2001 study by the National Injury Information Clearinghouse of the U. S. Consumer Product Safety Commission concluded that paintball is safer than bowling. The study noted that for every 10,000 participants, paintball involved 2.4 injuries but bowling involved 4.7 injuries.
It Depends on how fast you pull your “trigger finger.” On average 200 paintballs should last 4-5 games.