And the helium will give the kite extra lift in light winds.
Seriously, I use a rechargeable electric air pump made by Sports Air. I don't know if they make it anymore. It is a little bit smaller than the other pump pictured (I saw one in use and it pumped the kite up pretty firm). I still have to use the hand pump to get the bladders firm. I only use it for my larger kites 19.5m & 21.5m.
Regarding warming up (and stretching), definitely in colder weather. It helps prevent muscle cramps and spasms. Especially for us old guys.
Cheers,
Jake