I'd stick to one plant just because you can more easily manage to get one plant to grow into the footprint of the light and it's less work to care for one. You *can* do multiple little plants, but there will always be one that grows bigger/faster than the others, and often one that will be behind, one that will want more or less nutrients, etc... it's just more work and hassle for very little (if any payoff) if growing from seed.
But I only grow 2 at a time under a 600w, so I know I'm biased to less numbers and bigger/bushier plants. It's really just a question of style or technique and what you want to do in the end though. For example, if you want to try multiple auto strains at one time or if you are doing a micro-SoG w/ clones and 12/12... there's just so many different ways to do things.