Paul,
I have no specific experience of the Sherbourne, but in 2009–10, I built another, and not dissimilar, Caldercraft kit, namely HMS Pickle.
I found it to be a top-notch kit, with all parts and materials clean, sharp and of excellent make and quality. As for the instructions, they were incredibly good and included several sheets of very clear, full-size plans, together with a 64-page (if my memory serves me correctly, but something like that anyway) set of very thorough, step-by-step build instructions, illustrated with clear colour photos and written in excellent English (by, I'd say with almost total certainty, a native speaker of that language).
Based on that experience, I do not hesitate in the least to unreservedly recommend Caldercrafts period ship kits.
My only very minor caveat is that, as I haven't built another one since, I wouldn't know if they've kept up their very high standards from ten years ago, but I have certainly not heard anything to the contrary.
Mattias