I can just share what we have been/are doing and what I've read on SCM. We actually did HWT Pre-K when he was about 5, since he was trying to write on his own. Very gentle. We just did one letter a day, it was only capitals & practicing for those ie. lines, squares, circles etc. Lots of colouring too.
After that we moved onto HWT K which reviewed capitals first then moved onto lowercase letters. During the review of capitals, they introduced 3-letter words to copy, only 4 on a page. Also, we did only one letter a day, not using any extra practice on separate paper, just what was in the book. The lessons were probably 3mins long. With the lowercase letters, short words were also introduced during the book, as well as 3-word sentences, using the letters that had already been learned.
My son is now 6,5 and we will be starting HWT 1 soon, which focuses on lowercase printing, but more words and slightly longer sentences will be introduced during it. My son has also been doing Sonlight Language Arts K, which has daily copywork. However, I have noticed that he 'forgets' how to write some of the letters so I'm looking forward to using HWT again to give him a chance to review each letter individually and practice it.
Having said all that I did not know about CM during this time so although I tried to get him to execute his letters as best he could, I cannot say it was 'perfect execution'. I have seen his writing improve so much though since we started. My point is that it seems words and very short sentences are introduced soon after letters have been practiced and are not kept until the child is writing perfectly. How 'perfect' can a six year old boy write?
In SCM's H&R,T&W, it says "...letters should be formed into words as soon as possible for the child to copy. The goal is to write the word once without a mistake."
So, you could possibly have him start with reviewing his letters, both capitals and lowercase, but after a few, introduce easy words using those same letters he has reviewed and is familiar with, and that he is copying 'perfectly'. And slowly move to short sentences. Or if he has mastered the individual letters and is getting bored, then move onto words & sentences. I think the main thing is to keep it short and move at the child's pace.