Marg59 Make sure that you get all the relevant certificates well in advance so that you know exactly where you are looking for. There are lots of folk on RootsChat who can help with finding places that no longer exist or have changed their names.
Some of the places mentioned in this thread - Auldearn, Boleskine and Abertarff, Dores and Inverness - are parishes. Auldearn is in Nairnshire and the others in Inverness-shire, between them covering the whole of the east side of Loch Ness and the River Ness, plus quite a bit more around the south end of the loch. That is quite a large area and you need to pinpoint where you are going in that area before you get there. There are parish maps and descriptions in the county pages at
https://www.genuki.org.uk/big/sct (you have to scroll down to the list of county names - clicking on the map doesn't work).
You can read the parish articles from the Statistical Accounts of Scotland at
http://stataccscot.edina.ac.uk/static/statacc/dist/home. These gives a lot of information that will help you to understand what it was like to live in any of these parishes in the 19th century.
Errogie is an area in the parish of Boleskine. There is a tiny village - see
http://www.geograph.org.uk/gridref/NH5522 and
https://www.geograph.org.uk/gridref/NH5622 - on the shore of Loch Farraline. Errogie House is north of the end of the loch - see
https://www.geograph.org.uk/gridref/NH5623Farraline is on the east side of Loch Farraline - see
https://www.geograph.org.uk/gridref/NH5621Gorthleck is a short distance south-west of Loch Farraline - see
https://www.geograph.org.uk/gridref/NH5320 and
https://www.geograph.org.uk/gridref/NH5421I am not sure exactly where 'Moor of Errogie' is. I suspect that it was a name originally applied to all the crofts beside the track north of Loch Farraline and Errogie House.
For gravestones try
https://sites.google.com/site/highlandmemorialinscriptions/home - but of course that only helps if (a) they had gravestones and (b) someone has gone out and recorded what was on the stone.
There should be burial records, which will be in the care of Highland Council. Have a good rake through the catalogue of their archives at
https://www.highlifehighland.com/highland-archive-centre/ and if necessary arrange to go there when you arrive in Inverness to view the records - if you discuss it with them in advance they will have them all ready for you when you arrive.
You will have to hire a car and you should get decent maps - the Ordnance Survey Landranger series as a minimum. Do
not attempt to rely on Google maps or (even worse) a satnav!
You are legally entitled to walk over most land in Scotland, provided that you do no damage and do not put yourself or anyone else in danger, and you do not infringe other people's privacy. The same does not apply if you are driving, however. Just in case you want to walk where your ancestors did, familiarise yourself with the 'Right to Roam' by reading up on the Scottish Outdoor Access Code
https://www.outdooraccess-scotland.scot/