Mark:
My wife and I traveled for 2 weeks in Scotland on the train this past April 28 to May 15. We purchased a Spirit of Scotland pass for use over 8 days within 15 calendar days. It worked out great. We made a counter-clockwise journey from Edinburgh to Inverness to Kyle of Lochalsh. We then hired a private driver to the isle of Skye, took 2 consecutive day-long tours on Skye, hired a private driver to the ferry at Armadale, took the ferry to Mallaig then resumed our train journey on the Jacobite Steam Train to Ft. William. The next day we hired another private driver to visit Glen Coe, Inveraray and on to Oban. At Oban we took the train to Glasgow. We also used the train for a day-trip from Glasgow to Stirling/Falkirk and back to Glasgow. The Spirit of Scotland pass isn't valid on the Jacobite Steam Train, but we used it for all other parts of the journey, except where there were no trains available.
We stayed mutliple nights in Edinburgh, Inverness, Portree (on the Isle of Skye) and Glasgow, and stayed 1 night in Aviemore, Ft. William, and Oban. We did have advance booking for all lodging. As noted by others, booking lodging in the smaller towns could be difficult this near August (and in Portree very difficult, if at all). You could do something similar to our journey, e.g., a counter-clockwise journey, except perhaps limit your lodging to Edinburgh, Glasgow and Inverness (omiting the train from Inverness to Kyle of Lochalsh and the Isle of Skye)
Inverness, is a reasonable gateway for day-trips to Ft. George and Culloden, or maybe Nairn, or perhaps into the Caringorms, or to Ft. William (by bus). While in Inverness we took a half-day trip (technically a tour) on a brief bus ride to Loch Ness boarded a boat to Urquhart Castle and there returned to Inverness by the same bus. It was quite enjoyable and we didn't feel like we were on a tour. if you decide to do this be sure to have a cup of the "electric hot chocolate" on the boat to Urquhart. In inverness we had dinner one night at the Mustard Seed. We ordered from the "Early Evening" menu and the food was delicious. Try a "Woo-woo" cocktail.
You could visit many wonderful venues if you had lodging in these 3 "larger" cities and made a few day-trips. Importantly you wouldn't be unpacking and re-packing luggage except for the 3 city stays.
By the way, unless you've already booked your 1 night in Glasgow and it is non-refundable, why not head straight for Edinburgh when your flight arrives in Glasgow. You could take the express bus to the train Station in Glasgow and the train to Edinbugh and be in Edinburgh Waverly within a little over 2 hours after picking up your luggage in Glasgow.
Enjoy Scotland.