We cut our holiday short on the NC500, numerous factors but mainly due to the weather. We were grateful that we had not booked anywhere apart from the first 4 nights as we were able to change our plans at short notice.
Whale watching from Gairloch was cancelled due to the weather, zip wire at Durness closed due to the weather, Smoo cave tour not running due to the weather, can you see a trend! I know we were just unlucky with the weather can't do much about it but it really spoilt everything we were looking forward to.
One thing you need to do though if you can is going on one of the tours offered by
Caithness Seacoast — Exhilarating Speedboat Trips, Caithness, Scotland
Cannot recommend highly enough, William the skipper and tour guide was amazing and so knowledgeable about the local wildlife and well worth the money.
I would recommend not booking any campsites, none were anywhere near full even in August that way you can be entirely flexible.
It also takes far longer to drive between the places on the west coast than google will suggest mainly because you are driving slowly to appreciate the scenery and stopping to look at the view.
We will do it again but not for a few years yet and will wait until we don't have to take our son with us. We want to go back in June or July when all the migratory sea birds are nesting on the cliffs in the north, must be an amazing sight.