Best way to get to Cape Wrath is get a train or bus from Edinburgh to Inverness and thence Lairg. Get a bus to Durness and walk or hitch to the Cape Wrath ferry (Could be a bus to the road end, but probably very inconvenient). Ferry and tourist bus to the Cape Wrath Lighthouse. You can plan from Edinburgh airport using this. You may need to put in intermediate destinations, as you probably need to overnight. (Or from Glasgow...everything just seems easier to me from this side of the country, but it may not be,)
https://www.traveline.info/We may be going Cape Wrath way in October as they have re-measured a new Sub 2000 hill there, and it appears to have the correct criteria to be a new Marilyn Aaaargh. At the moment intending to take the Cape Wrath bus and getting off.
From Durness to ferry terminal is just over 2 miles. Ferry times vary with the tides and you can only find out from a notice at the terminal, or by phoning the guy 07719544207