Paintball guns can use Co2 from any company, they are all built the same. You can find valved tanks and 12 gram's at sporting stores, paintball fields and proshops.
Yes, the largest CO2 tank, the 24 oz can fit on the Brass eagle Raptor or any marker for with standard ASA threads. However not every marker can use Co2.
Which brass eagle?
No. Brass Eagle products in general do not last very long before breaking. This also goes for any guns you can buy at Walmart.
Any CO2 tank with standard threading. It cannot use un-threaded disposable 12 gram cartridges without an adapter.
you need Co2 to fire any paintball gun, it is what physically moves the ball out of the barrel.
No. Not without significant modification at least. You should look into upgrading to something.... not plastic.
No there is not.