Which category

That will fall under the basic category, namely 21%.

I actually mean which costs? Are these small purchases of all kinds?

Small materials & tools if you use those products in your practice. If you sell them, they are trade goods. It is up to you to decide where you will make your main profit: Sale of products = products are trade goods / Care = Small tools and materials. These categories are mainly there so that, in the event of an audit, it can be verified whether your story is accurate. If you bring in very large quantities of cosmetics as operating materials, you will be asked what you do with them. If there are no outgoing invoices to state, it will be assumed that you are selling them on the black market.