You may wish to revise your altitude of....
"as long as I have more than 500feet over terrain I reckon that should be ok. (I really want to fly over all mountains, no valley or contour flying !)"
To more like a 'cuppla thou' above terrain, for the reasons Mr CS gave, and to have a wider field of vision, and to enjoy the trip more, just in case....
Be very mindful of the effect of the wind on turb generated.
ENJOY - and tell us how it all went, ....
Cheers
Sorry Uncle...was right 'on top of you'....