For the .177 & .22 you get around 32 full power shots, with the .25 caliber version
it's around 16 full power shots.
You'll need either a HPA hand pump, such as a Hill, or
a HPA tank(SCUBA / etc)
You will also need to buy the adapter which connects your HPA source
to the rifle.
The number of pumps necessary to fill the rifle will depend on how far you shoot
it down(1500psi? - 2000psi?). And which HPA pump you're using, since some are more efficient that others.
But, generally somewhere from around 50 to 70 pumps.
Added - for what it's worth
IMO, the .25 caliber Marauder is the only one I would buy.
If you prefer the .177 or .22 IMO it makes more sense to buy the
much less expensive Discovery. Especially if you plan to use a
HPA hand pump. the Discovery fills to 2000psi, compared to
3000psi for the Marauder
Depending on the pump, 50 to 70 strokes should deliver "around"
32 full power shots in either .177 or .22. Whether you get 900fps,
or more or less will depend on the weight of the pellets you're shooting.