Then the choice is yours, if you spray it in parts and take the proper steps like putting masking tape on the edges of doors and glass etc. when you put it back together when it's dry you will have a much better job. The inner door posts won't have over spray and your windshield area will be sealed (they would if you jambed the openings, just making sure you paint them). If you do decide to paint the car in pieces take extra care and caution when you but it back together, get help with the bigger pieces like doors, hood and deck lid and you'll be fine.
If you want to paint it all put together that's OK as well, just mask up what you can, engine bay, under hood, trunk and door jambs.
Hope this helps.