as said above, the prep work will take the most time... especially if you are going with a gloss finish you'll spend a long time getting the body straight. Masking properly will take more time than painting.
Since your jeep is a dark color I would primer it white or gray first before spraying a lighter color over it. If you are going with a flat finish, I would just get some scotch-brite pads and rough the paint up, you shouldn't need to sand it down too much unless your paint is really rough. If it is, sand the rough areas with 300 then 500. for gloss finish do 1000 after that. make sure you sand down all the areas that clearcoat is peeling or powdering up, they'll keep peeling under the paint and ruin your paintjob.
lots of light coats will come out much better looking than a couple of heavy coats, how good are you with a spray can? remember not to start or stop spraying facing directly at a body panel, you have to turn your wrist towards as you start and away as you end, unless you are starting and stopping off the body. I can come by and show you what I mean if you want. a good distance is 12-18" away to avoid ending up with stripes in the final product. let it dry at least an hour before you throw another coat on, 2 if it's cold or damp outside.
Be prepared for paint dust to get on EVERYTHING. not just in your garage, outside as well as the fumes go out the door. Don't paint with the garage door closed, and at the very least wear a mask that covers your nose and mouth, googles that seal against your face is a good idea too for keeping paint dust from the air out of your eyes.
I've painted a dozen or so cars with spray cans, if you take your time it can come out really well. Stick with a good paint like krylon, duplicolor, or rustoleum. Cheap paint doesnt stick as well and the color fades quickly if it sits out in the sun all the time.
Good luck