Hi, James and Dr. Udawat
First of all, Aberdeen is, for the most part, a beautiful city. It has many parks, many historic buildings, and it's situated between two attractive rivers. It is definitely a tourist destination, and is the gateway to Royal Deeside, the Grampian Mountains, many castles, and many beaches. The only down side to Aberdeen is the Trump golf course, but fortunately, that's outside of the city. Unfortunately, the Aberdeen train station is in a singularly unattractive part of the city.
Most tourist guides, including, unfortunately, the RS guide, do not mention Aberdeen at all, or just in passing. When visitors come to Scotland, if they are unaware of the beauty of the east coast, will only visit Edinburgh, the Highlands, and the Isles of Skye and Mull. There is so much of beauty to see in the northeast. However, it works for visitors like me, as the lack of tourist information keeps the lodging prices low. :)
That said, Dr. Udawat, you are planning quite a lot for your time in Scotland. If you are basing yourselves in Aviemore for your entire time in Scotland, then you are going to be doing a lot of unnecessary traveling by rail. For instance, taking a train from Aviemore to Aberdeen would involve changing trains either at Inverness or Ladybank. To travel to Kyle of Lochalsh would again involve changing trains at Inverness.
In addition, the major cities - Edinburgh, Glasgow, and Aberdeen, need more than a day trip. Also, you have to factor in the fact that you'd have to include the time for the return train to Aviemore.
Unless you have your hearts set on Aviemore, it would be easier to take the train to Edinburgh; head up the east coast to Aberdeen; then overland by train to Inverness. Once you arrive in Inverness, you'd have the option of taking the Kyle line for Skye, or heading down to Aviemore at that point. You can also take the train from Inverness to Thurso for your trip to Orkney, but you have to take a bus or taxi to Scrabster for the ferry, then buses on Orkney. Finally, from Inverness you could then visit Glasgow on your way south, by way of Perth.
My very best wishes for your journey!