Many of the retail sporting goods stores will have refill stations for your cylinders. Also, I have seen hardware stores that will do that too.
Where did you buy the gun? Chances are that the store the gun was purchased from will be able to refill the cylinder for you.
No paintball gun will work without a CO2 tank or other propellant tank. without Co2 there is nothing to push the ball out of the barrel.
Where the air tank or co2 tank normally attaches
yes
There is no such thing as a "CA" tank.
A paintball gun, unlike airsoft or real firearms will have a hopper on top, and will have a co2 tank sticking out of the back.
you need Co2 to fire any paintball gun, it is what physically moves the ball out of the barrel.
No, any tank will work.
You probably could fill it, but not to pressures needed for paintball gun operation, CO2 tanks should not be filled with any gas or liquid besides CO2. edit: you could use Argon in a HPA tank but not a CO2 tank
unscrew the tank, this will vent any co2 that is in the marker out the asa
if your tank runs out take it to your locale paintball field thay should fill it up for you for a small fee exp=5$ unlimated air for the day at my field.
Take it to a shop! if you want to do it yourself the normal way is to put the bottle on scales and fill it from a larger bottle to a fill weight. To be honest though CO2 is well out of date. A smart move would be to move onto compressed air.
You cannot unless you have a gauge installed, or know the exact weight of the tank.