Lots of good information from the others and as I live in Wick feel free to contact me on anything or want some golfing company from Brora round to Reay.
Roughly in the direction you say the Inverness to Brora mainly about the golf apart from the sightseeng tours, and the detour to Bonar Bridge has a few nice scenic spots and was the main road before the Dornoch bridge which cut out 25 miles on my trip to Inverness. Fortrose is worth the visit to view the Dolphins and golf.
I'm surprised James never mentioned La Mirage for a fish supper!
The drive up the coast to John O Groats starts to get a bit more scenic but not as good as the West.
If looking for Hotels I'd recommend Mackays Hotel in Wick
The Old Pulteney distillery in Wick is worth a visit as it was Whiskey of the year a couple of years ago
[size=78%]http://www.oldpulteney.com/#[/size] While at Wick GC the beach too.
At John O Groats a short hike at Duncansby Head has nice views and sea stacks.
A short trip over to Orkney if you have time with great stone age sites.
Duncansby head, the most northerly point on the mainland.
Then Mey Castle as mentioned and the beach at Dunnet.
Ignore Thurso GC, just a goat track
After your golf at Reay the coast is littered with beach views and the scenery starts to become more interesting.
Smoo Caves before you reach Durness GC and there used to be a seafood van worth stopping for there.
After Durness heading down the coast the scenery is stunning.
The ceilidh place hotel in Ullapool worth a stop
[/size][size=78%]http://www.theceilidhplace.com/[/size]The NC500 mentiona Applecross, don't miss it and food at the Inn.
If you are nipping over to Skye I'd say its worth taking the ferry over to Mallaig and golf at Traigh GC a stunning walk to play golf.
That would lead you to Fort William, then up the Glen to try and get a peek of Nessie in the loch before Inverness.
Not quite the 500, maybe 750 but you have plenty of time.