I'd agree, go north if you want scenery and quiet roads. Midgies are not too bad on the east coast. Just avoid the NC500 which is full of idiots...
Maybe up to Inverness, then Black Isle, Cromarty ferry (check the timetable), Portmahomack, Dornoch, Lairg. Then back by Ardgay, Alness, Dingwall.
Could do another loop around south side of Loch Ness, Fort Augustus and back, though is a bit of a hill up and down.
Though yes, options for controls could be limited. Don't think there's much north of Inverness open overnight. Dingwall Tesco is open till midnight, or Tain till 10pm.