Very quick look:
Not keen on the clash of the old and new - would have been nicer (IMO) to keep the existing eaves.
Not keen on the angle in the plan - is there a reason?
CO to living room for stove.
Probably need eaves ventilation at roof junctions.
It’s a bit of a beast to be honest. I’m not that keen on the massing or the elevations especially the front door and the window above the door. Sorry but not my cup of tea.
Errr……why don’t you move the services to where you can get them out of the building?
Plus:
Connect the WC directly to an IC outside the building.
Connect each appliance to an external GT and then to an IC.
Vent the highest IC.
I think you should seriously reconsider the design. Take a look at the recent episode that Patrick Bradley did of a renovation of a clachan. I don’t think what you are doing is in keeping with the vernacular dwellings and is overpowering. Think about a more subtle way of renovating the buildings that will allow the original buildings to stand out and not be overwhelmed by the new proposals.