Once, and then don't walk on it. Since you are starting with raised beds, which presumably have not been walked on since they were made, I'd not get overly concerned about it.
There are, to be sure, contradictory opinions on this.
Some folks like to stir everything up - it feels like they are doing something. I'm presently of the opinion (having done the tedious double-digging thing with no particular effect/benefit) that the approach of leaving the soil as undisturbed as possible/practical and allowing the natural processes that are upset by enthusiastic tillage do their jobs is at least as good, and perhaps better.
If you are not walking on the soil, then roots and earthworms should provide all the loosening it needs. Feed it from the top and let the worms worry about moving that downward. If you think you have some sort of major compaction, you have on the one hand the option of mechanical approaches, and on the other using things with strong roots (such as diakon radish) to break it up.