once you have done the painting and left it to set for about and hour or two, you can put the wheels back on, carefully (with two people) and then take jacks away, car will be fine, if it rains you can cover the wheels up just in case!
Im doing this myself this week as is it supposed to be nice for a few days.
1) If you have a trolly jack, jack up car and place 2 axle stands under two front axles or jacking points and lower trolley jack, or use two jacks and jack both sides at same time then place on axle stands.
2) Remove 1 or both front wheels at same time depending on whether your doing one or both at the same time, my advice would be to do two wheels at a time, take off wheels then clean down calipers with wire brush/white spirit and brake cleaner/degreaser to remove all dust and crap.
I would also give your calipers a good scrubbing with wire whool to get them up nice and shiny and remove any rust or rough deposits.
3) Then start painting (im using hammerite smooth) with caliper paint or just hammerite in your choice of colour, try to build up the layers and not BLOB it on, you want a nice smooth coat with no drips.
Allow plenty of time between coats and just build it up until happy, careful not to get any on discs/pads etc.
4) Once happy allow a few hours to harden and carefully refit your wheels, i would allow at least 24 hours to fully harden and dry before using the car, as the heat will melt/chip the paint before fully cured.
You could apply a good few coats of protective wax such as poor boys wheel sealent to the calipers before refitting wheels as this will protect them further from the elements and will repel brake dust.
Then do the same again for the rear brakes, its a lengthy process but i would take my time and make sure you get it right.
