see south west Scotland (Glentrool, Clatteringshaws etc etc- see forest tracks, lots of, roads are quiet as well ), you don’t need to use the centres that are nearbyish, this is an overlooked, scenic and varied area.
(http://www.gallowayforestpark.com/)
to see (IMHO) best Scotland, do west coast by the islands, I stayed in Plockton (Skye, Torridon etc driveable) and loved it, however riding here I would suggest is harder and ‘less flexible’ as there just aren’t many places to bale out to (and track options)
also stayed at Grantown on Spey (near Aviemore but a bit less ‘touristed’), loved it, lots of riding and scenery in the Cairngorms. Some stunning and varied riding here.