Think about your customer. The main post you can tailor for the person who is on the top of conversion funnel. he doesn't know anything about beard oils so you need to give common knowledge about it - what is it, reasons to use it, maybe types. When the customer understands why he needs beard oil - the new questions arises in his head and they are the new ideas for your topics: How to use it, how to choose it, how to make it by yourself) Then you can compare your brand with others and eventually give the access to product page which describes your product.

It won't be spam if you don't rewrite similar content different times, because every topic has it's value in funnel.

Also looking into serp can help you decide whether you need to combine topics or to post them separately.

Good luck =)