Voicexml how many words in grammar

Question

I want to have a dynamic grammar in my voicexml file (read single products and create the grammar with php)

my question is, if there is any advice or experience how many words should be writte into the source from where I read the products. I don't know much about the structure or pronunciation of the words, so let's say

a) the words are rather different from each other b) the words rather have the same structre or pronunciation c) a mix of a) and b)

thanks in advance