We did a 3 week tour of Scotland a couple of years ago.
We booked through a company called Clans and Castles. They were fabulous to work with.
We gave them a list of things we wanted to see and a time/budget.
They took care of everything and made suggestions of things we might want to look at.
They specialize in historical tours and if have any Scots heritage they will point you to areas that might be of interest.
They put us in a guest house with ties to our history, which was really neat.
If not for them we would have missed Skara Brae, which was fascinating.
The company had everything done for us: lodgings, maps, tickets, ferry passage...it was all packaged up. But all it did was offer a framework: if we felt like skipping something, we could. We could stop and see what we wanted within the few fixed timings.
If you own a GPS, spring for the software package and take it with you. It made everything SO much easier. No fighting with maps, no worries about which exit on the round about....
Second, in Inverness, you may want to make time to visit the Highland Archives if you have any interest in genealogy.
Oh - if you are intrigued by rather cool Engineering, check out the Falkirk wheel, just north of Edinburgh. Amazing what 120 watts and some well executed centrifugal force can do...