So are all of the walls drawn as single lines being removed? If so, is it safe to assume that the kitchen will not be as shown? (An island sink is a bit bizarre - it's more usual to have the hob there, so that the cook can speak to people, and suggest they don't eat too many crisps
)
You may already have suitable "escape" windows in the living room, but if not, check what your BCO thinks about the design - AFAIK, strictly speaking the LR (new bedroom?) does not "open directly onto a hall leading to the entrance or other suitable exit" because of the porch. He might be OK with access to the porch, or through the house to the back door(s) or he might not - it's as well to know asap.
Why is the extension narrower than the main house? Problems building up to the boundary line? It creates an awkward looking step in the wall inside. What is it - 10cm or so? Not big enough to be useful, it'll just look a bit off, and make fitting skirting boards, flooring, and coving (if you have it) fiddly. Given that (another guess) you've got to keep that 25-30cm bit of the existing dividing wall for structural reasons, I'd be tempted to board out the run between there and the extension so that you have a flat wall all the way.
Re the roof - it's going to be pretty gloomy at the back of the new open-plan space - it'll be 10m from the openings at the back of the house. If I had to make one suggestion it would be to give serious consideration to a
roof lantern.
OOI - what tool did you use for the plans?
Lastly, re the image posting problem, you needed to do
steps 1,
2,
3,
4,
5,
6,
7,
8 and steps 9,
10 &
11, not just the first 8.