? about CM style beginning reading

For the word building exercise, CM stated in vol. 1 that the word ‘is’ gives no new word.  I thought ‘his’ would come from ‘is’ but are you only supposed to word build when you can take part of the word away?  So the word ‘and’ wouldn’t make any new words either?

Also in the poem “Rain”, you have the words ‘rain’, ‘raining’, and ‘rains’. Do you treat them all separately, with three separate bases to build from ‘ain’, ‘aining’, and ‘ains’?

Then do you have all the newly made words preprinted on paper strips to add into the mix of your poem words or do you write them on strips as your child learns them?

Do you teach proper names as they come up in word-building exercises, ex: rain – Cain or tree – Lee?

What about words that are more old fashioned, aren’t used much, or you will have a hard time explaining what it is to your child or they may have a hard time making a connection with it?

I guess I’m just wondering if I’m supposed to teach EVERY possible word that can be built or if it is ok to edit a little bit.