I know we have the combines and reports on various college kids, but when does free agency start
You're thinking in the right direction.
If you buy into Dennis' and Rod's "best player on board" drafting philosophy, logically, we should be filling key position needs in free agency to remove the pressure and temptation to reach for need during the draft.
The practical application of this strategy would be: If we need a couple of dominant linemen (at any of the 5 positions because we can always shift the other guys we've got around), and can land both in free agency, we won't have to pass up a highly regarded QB, RB or NT draft pick in order to plug a hole at tackle, center or guard.