How long are the trips for? If it is a week, don't try to cram too much in. We often hear of road closures in Scotland, with one diversion in place...of 46 or 75 miles etc....in short, much of it is big and empty...of both people and roads. If you want quirky and unusual cross to Skye on the Glenelg ferry, the worlds last surviving manual turntable ferry through a narrow sea channel with turbulent water. A great experience.
If it is a search for great roads, there are better roads than those that make up the NC500. Look at a decent map of the top 1/3 of Scotland, the NC500 goes right round the edge....thru the middle are some amazing quiet roads, single track with passing places that emanate from Lairg (fabulous cafe there..
https://www.pier-cafe.co.uk/ )
Depending on how many of you are going and what distance you want to ride daily, it may be beneficial renting a decent big property somewhere around Inverness. Then do day trips....one to Skye, one or two North, one or two to the Cairngorms etc. It means you get to see as much riding and scenery as you want, but without the need to carry your kit day by day, and also you can look at weather and head for where it is better on any given day.