Thank you all.
I did have a look at The Man In Seat 61, but found it more useful for Continental rail Bigdog.
Cheapest journey is definitely East Coast Aberdeen to Edinburgh (I really like East Coast First), then TPE.
Because this is a leisure trip I really am being a Scrooge and £106 compared to £252 return on East Coast via York etc, is too much of a difference.
I did wonder about the TPE rolling stock as well having travelled from Manchester airport into town on their trains many times – they are not built for long-distance travel.
Oh well, seems like a comfier seat and a cup of tea will be my lot – I’ll get fed and watered on the East Coast sector and fill my bag with their goodies!