In some part, we can help but we can’t customize the template for you, for example, we can help you to change color, size of fonts, bg colors etc, mainly things that are related to css,
No, there is no single line of the code that can be considered as a junk, everything is necessary
Seo - i think you misunderstood how SEO works, this is hml template it doesn’t have any SEO tools such things are totally on you
pages - everything is already created you can reuse existing elements on the new pages this will require some level of knowledge in HTML, if you dont have this level i can only suggest some free courses, unfortunately, we can’t help you in designing and creating page