Hi David
I can't comment on the other locations but as for Linn of Dee I know it well.
Mar Lodge just after Linn of Dee has in recent years been very welcoming to challengers. Including providing both bunk beds in the Stable block (hostel type accomodation) and allowing camping just outside the big house.
There has been in recent years meals supplied and coffee and biscuits around a big fire in the gun room making this a challenger haven and just the place a newbie would like.
I do believe that part of the reason they do this is that they would prefer that challengers (or hikers in general) do not wild camp along the banks of the Dee or in the imeddiate area of Linn of Dee as this area is already heavily affected by visitor numbers. (I definitely wouldn't feel like wild camping for that reason).
If you wish to wild camp I would suggest stopping at White Bridge or heading past Mar Lodge down to the Quoich.

Colin

Many thanks Colin, and to others who have responded - I have received a number of e maild direct. Challengers are clearly a helpful and freindly bunch - if off divided opinions sometimes in relation to answers to my questions. But all very helpful, so thanks again all.