Is it really going to be so costly to repair and renovate? What actually needs doing?
It is listed, and not only listed, but Grade A status, so of national importance (Here's the listing hsewsf.sedsh.gov.uk/hslive/hsstart?P_HBNUM=29263). You'd need permission for all alterations, inside and out, and this does mean that specialist techniques may need to be used, which as a rule of thumb doubles the ordinary cost. That house is so special that perhaps you have to triple the ordinary cost. You might be able to talk to Scottish Heritage, SPAB and the local Conservation Officers (or whatever the scottish equivalent is) about it to get a better idea.
In terms of altering the floor plan, I'd guess you wouldn't be able to take out any walls that aren't modern additions, or move or add any doors, but you could put in new walls, although they'd risk spoiling the proportions of the rooms.
I can see it needs central heating (at least, I can't see any form of heating at the moment), which will then mean that you need re-plastering (by a specialist firm) and re-decoration throughout. You'd need listed building consent for that.
This is going to sound absurd, but I wonder whether it's large enough - or rather, if it has enough usable bedrooms and toilets for a family. If you have a look at the floor plan, it seems that the layout on the ground floor is okay as it is - kitchen, dining room, sitting room and study. You remove the shower from the study. I'm assuming that the kitchen would benefit from being re-fitted, but it might be fine. There are no loos on the ground floor, the kitchen is rather small (no room for a table) and there's no utility room, but it's not a bad layout at all. If the division between sitting room and study isn't original, you could take that wall down too, perhaps.
Then, on the first floor, you remove the second kitchen and turn that into the family bathroom, accessed via the 'breakfast room' (or 'breakfast room' becomes a family bathroom and 'kitchen' becomes a very large en-suite). You remove the current bathroom (assuming that's a modern addition) so that Bedroom 2 returns to its original proportions. One of your children goes in the current Master Bedroom, one goes in Bedroom 2, and you and your DH take the current 'family room' upstairs for a truly vast bedroom. Hey presto, three nice light bedrooms and one bathroom / toilet. You might even be
The second floor is more tricky. Bedroom 3 and Bedroom 4 look as though they're going to be very dark to me (former servants quarters, presumably). I don't think you'd want to use them for family bedrooms, though one could be a guest room for occasional visitors and one a play room to get the kids out of the way of the lovely sitting room and dining room. It does have another shower room / toilet. Bedroom 5 is definitely on the poky side - just a glorified boxroom with a window, really! Plus I bet it's freezing up there in the attic.
Here's an interesting article from last time it was sold
www.telegraph.co.uk/property/propertyadvice/propertymarket/3316102/Beyond-the-Fringe-the-wreck-of-ages.html
I don't know whether all that puts you off or encourages you!