I suggest changing out the Win key for System/Super/Code, and the Menu key for System/Super/Code too
Double 1u Ctrl isn't necessary; one of them can be safely removed, or moved to the add-on kit for ortho support.
Consider using R3 \|, R4 <> for basic ISO support in the base kit, and keeping all of the UK keys grouped together in the add-on kit.
See how Tidal did it. More on this topic
here.
In short: move R3 #~, R4 \| from base to add-on, move R3 \| from add-on to base, add R4 <> to base.
Not sure how useful a R2 num = key is. R1, sure, but R2 — dunno, you might want to remove that.
Is that accent legend color seen on Esc and Enter the same as the alphas legend color?