TBH – some of the road sections are “less than pleasant”, and I say that as an experienced road tourer. Certainly stay off the A9, and the A84round Loch Lubnaig is a bit of a race-track.
Are you sure you want to go North-South? I’d say that heading North was a more pleasurable experience and you are also then likely to have the wind behind you all/most of the way.
Loads of accommodation in Aviemore. The Bunkhouse seems to get decent reviews and I always recommend the Cairngorm Hotel if your budget will stretch to it. There’s a nice wee cafe in Carrbridge too – good cake and soup.
If you end up stopping in Blair Atholl, Dalgriene Guest House gets my vote. Very bike friendly. Decent food at the Atholl Arms too. I don’t really like Pitlochry or Callander – just too busy/too touristy. But then that also means you have lots of choice when it comes to rooms and food.
TJ – I’m assuming that road bike = 23mm