DIY quality paint job

spraying all at once, as in the whole car at once vs. one section at a time?

Yes, because of the difficulty of changing the thinner in relation to the changed weather of other days and because frankly paint is great about getting airborn and sticking to particles in the air dropping them back to earth, after about about 20min of spraying your garage is nearly particle free lol, and atleast this way the inevitable particles stay hidden under several coats of color