We briefly ran our 1200 vacs and VR drive all off of one outlet last year.  Our antique tractor did not have enough hydraulic capacity to provide adequate raise and lower performance with this background load, so we opted to add a pump on the PTO which now runs the entire planter load  all the time.   The tractor ran the planter fine in the field, it was on the end rows that everything started to fall apart because there wasn't enough oil to go around.   This added pump provides 40 gpm and it is all delivered to the planter through one hose, and allocated to various functions by the valves on the planter.  The way we are set up is with two vac fans in parallel and the PWM valve for the VR drive also in parallel, with the bypass (excess) flow port blocked off. I originally did not think this was the correct way to set it up, but I was convinced that it was preferable.  When the VR drive shuts down, it deadheads the flow which is normally running it and increases the flow to the vacuum fans somewhat, which increases the vacuum level while turning, the theory being tha this will further discourage seed from dropping from the disks.  As soon as the VR turns back on, the fans slow back down to where they are set to run.    The only downside is that the fans need to be set in view of operating conditions, not static, parked conditions where the VR is not running. 

The 1790 Deere we had before had all sorts of stuff doubled up...both vac fans were on one outlet, which could have been power beyond if needed, the CCS fan ran off of the back side of the raise and lower circuit,  and if it would have had VR drive I believe that would have been piggybacked onto the CCS circuit.