Multiple domains, different sites to boost an ecommerce page

I'm not sure how to phrase this question. So here goes an explanation.

Let's say I sell burgers and I own americanburgers.com. This is the ecommerce site I want to rank. I sell burgers online.

But I also bought cheeseburgers.com, baconburgers.com, healthyburgers.com, etc....

We want to experiment some SEO techniques (black, grey, whatever), but we don't want to risk hurting americanburgers.com

How could we leverage baconburgers.com, cheeseburgers.com to improve the overall presence of americanburgers.com?

Here are some ideas:

• Multiple blogs that create backlinks?
• A dropshipping site?
• A branded alternate site that is a hub of knowledge about burgers in general?

Is boosting americanburgers.com the right goal? What should the goal be when you have several domains in the same niche?
I tried looking online but what I found was related to multiple domain redirection, how to set it up etc.

I'm looking for a pointer here

Thank you.