I am migrating to a new domain, the previous domain that I had it was really just used for me to learn how to develop websites, so the traffic, if any, of the old website is not important for me, the problem here is that now I am concern about the new website SEO, I do care about this new domain and since the new website is going to have the same information as the old one, I was wondering if google is going to penalize my new domain for having essentially the same content of the old website. I did implement a sitemap, link it to search console and even had analytics, just for testing idk if this information is relevant for the issue, but just to point it out.I am also using a default header file for every page in the website, so since SEO takes into account the title and the description of the page, should I stop using this default header? or there is a way to overwrite the information for each page. I am using php require for header and footer files. 
New domain SEO and default header file
seo;domains;html;php