If there were differences in dress between kingdoms I don’t know of them.
I’m fairly sure there weren’t any regs about tunic length
Nasal helm fine by me – NCS pointed out the sources seemed not to support the drawing in Heath’s book.
Bare legs/leggings/trousers – conjectural and unknown bar some marginal cartoons of lower class infantry in manuscripts. Bare legs unlikely I would have thought for a nobleman.