Are 10m boundary constructions allowed in NI?
Not that I know of
Yes, it would already help here if one used a standard floor plan without the expensive living room bay.
I think so too.

I also don’t see the wishes/extras here. Backup kitchen, there is no space for that. Direct accesses or everywhere, doors that are only needed for connection or as an airlock, I don’t see either because they steal space and room for furniture. A utility room/freezer, which is also supposed to serve as a laundry room with sink and storage room, can hardly still function as an airlock. Guest WC, which is meant to be used in old age (probably why the guest room is so large), would in my opinion need more space to be used as a main bathroom for the infirm. Then I read about switching children’s room/parent area. You immediately know from that that the children are not yet there and the view from the parents’ bedroom is meant to be celebrated. Classic house without frills works, I think, wonderfully. The annex doesn’t make sense anyway, not even with “view,” because the living space is retreat, and you don’t stick on the sofa in the house to watch the panorama. You don’t do that on vacation either. Here the stay in the garden must and should not be underestimated. There is no time for idleness there.