In 2011, with a friend, I did Durness to Dover over 8 days, so an average of 100 miles a day, to raise money for East Anglian Air Ambulance. North to South, on the basis it was more downhill!
Looking at your route, on day 4, by veering north-west, you're going through hillier countryside than if you stayed east of Doncaster, but I guess that ties in with staying with your parents?
For days 9 & 10, wouldn't following the cycle path along the A9 be easier?
It amazed me just how big Scotland is - and how empty the roads are compared with the south-east. Enjoy!