We will be picking up a car in Edinburgh to travel to Skye and the Highlands. We would like to drop the car off in Scotland and proceed by ferry to Ireland (Belfast or Dublin) then pick up a new car in Ireland for the remainder of our trip. Any suggestions on best places to get ferry to Ireland?
You can get ferries at Troon and Stranraer. Troon is probably the most convenient given the places you mention. The ferry will take you to Larne and I am sure you can arrange a care rental there quite easily. If you intend going to Eire, make sure the company you rent from allows you take the vehicle across the border and the insurance covers you in both countries.
Just a word of caution about rental cars in Ireland. Every place else we've rented a car (all over Europe and the UK) husband and wife are considered kinda of a unit. In Ireland for me (beloved and oh so lovely wife) to be added on as a driver incurred an extra fee which, as I recall, was o/a $200. Check it out ahead of time as perhaps things have changed. Would appreciate any feedback from the Wall as we are planning on returning next year.