Install WordPress in a site that is already done can cause any issue?

My website was made by a guy 3 years ago and has never been changed since that time, the site looks older.

I have a really good domain that ranks me in first place on organic search in my service. But there are other keywords that I could add to my site and catch more clicks.

The main question is: I would like to install WordPress to make changes to the website. Actually, I already created a brand new site in a localhost using Elementor (following all SEO Rules). The site looks 10x better than the live one.

I'm not an expert, and I am afraid to make some Sh** and lose my website on organic search.

My domain is the name of the product I sell, I thought to buy another domain with my company name and add this new website that I created, but I read that is not so good to have 2 websites with the same information.