Spot on mate. That's a really good observation and concerns me too. Especially the Van Gaal part since he has to impose his total voetbal philosophy on the team.
And being a trainer coach he'll have to dedicate countless hours at Carrington unlike managers with a more hands-off approach.
The FA should seriously consider a 4 week rest through the strenuous Christmas-New Year period like the Bundesliga or atleast 2 weeks like La Liga. The current system places too much workload on players and managers - I think it's when most players accumulate injuries. Particularly at a club like United that normally competes on 4 fronts.
In a way it's beneficial that we don't have CL football next season. Van Gaal can have a good lie-down period in between domestic fixtures and through International friendlies once his training system is in place. I think Giggsy can really endear himself to the manager by easing his burden during training, plus it'll be good for his own managerial education.