Hello again,
Tain-Edinburgh is roughly around 130 miles and the A9, Scrabster route, will take between 4 and 5 hours depending on your speed.
As you point out you are big
scenery and nature lovers, the route from Tain to Edinburgh through Aberdeen offer you beautiful landscapes.
When you reach Aberdeen and take in some more of the areas landscape follow both the A92 north from Dundee and the A93 from Perth towards
Edinburgh.
Happy travels