Thank you for the detailed response!
In terms of the first 6 questions:
1- Do you have PP or can you still mess change it easily? We are looking to go into planning in the next 3 - 4 weeks.
2 - Are you in a regulated area eg conservation or eg listed? Conservation area
3 - What standard are you planning to build to? If it is anything like well insulated you will have thermal and solar gain issues with all those south-facing windows and skylights, never mind the aggravating factor of having the proportions of a bent narrowboat broadside on to the sun with essentially a glass wall on that side . Yes this is a challenge, hence the architect.
4 - Skylights? Personally I think those skylights look not-very-attractive and a bit scattergun. We are going to align them as best we can, the master bedroom one we will change, it is tricky as our architect does not think we will have any hope of having the plans agreed with them on the other side.
5 - Is the back straight on to the street? Yes
6 - Are your slates reclaimable? On the front of the barn no, on the back yes.