Some excellent roads up there. Once in Scotland just avoid motorways.
Regards eating I've always found 'The Horn' at Errol - just off the A90 between Perth and Dundee to serve a good bacon roll. You need to come off the A90 but it is well signed as I recall. BTW if you are using the main route Dundee to Aberdeen watch your speed it is littered with speed cameras and is a well known racetrack for neds (the scottish equivalent of chavs).
A scenic route I have used is a bit longer and misses the Horn.
Glasgow - Crianlarich A82
Glen Dochart A85
Killin A827
Aberfeldy
Pitlochry then the A93 through Braemar and on to Aberdeen.
A bit of a long short cut but some excellent scenery and good roads.
Hth
Edit :- I think the road numbers are correct but its a wee while since I've done this route but they are very close.

jealous as I'm going up that way in a couple of weeks but will probably have to take the car.