I want to break up my products in such a way that I can rank for a variety of keywords.
But it will result in more than one category having some of the same products in it.
For example, I want to have a "small" category with my small products and I want to have a "walnut" category with my walnut products. But the product that is both small AND walnut will be on BOTH pages.
Is this ok? Will google penalize?
ps. there will be no instances of absolutely IDENTICAL pages in my site structure plan. Just a few products overlapping.
That is a great question that you have asked about categories and Google penalties. In short, Google won't penalize you for using category pages on Shopify even if your products have multiple tags attached to them. The only case where you may run into issues is if your category includes the same products as one of your collection pages. This can cause some issues with Google's indexing as it would look like duplicate content. You can learn more about that here: https://gofishdigital.com/how-to-fix-shopify-duplicate-content/
I hope that helps answer your question! Let me know if you have any further questions that I can help you with.