You can do either. I prefer one at a time, cause then you can put the camera anywhere you want, without risking other cameras being in the shot. Same with lights. If there is just one camera, it gives you more options of where to put the lights, as their is no other camera, to have to work around, when deciding where to place them.
In my experience though, the other directors I have worked under so far, prefer more cameras, so it all depends on you. But multiple cameras results in compromised angles, like you would see on a soap opera or sitcom. Compared to movies, where you can put them less compromising places, but it depends on what the storyboards call for as well, as to whether or not you should use more than one.