ask away bud, thats how you learn.
im assuming its a 3000psi bottle. roughly id say around 4pots.
getting ur air tank really depends. firstly you have to dinf out weather your local site can provide air for you,as some places only do co2.
if the site does provide air, the price is usually included in the price of the walk-on or day of play.
alternatively some sites ask for a 5pound fee and you get unlimited re fills.
if you go to a scuba shop,its expensive at around 2quid a fill..
so it all depends on your local site really!!
is the ion reliable?? well ive had 2, and not had a problem with any of them. if things do go wrong, its usually very cheap to fix compared to other markers such as angels.
the ion however,does not like flat batteries,so a new battery every 10-12 cases of paint is recommended.
other than that,not alot can go wrong with them