The way I understand your question is you are building a one page parallax type site but you want the navigation sections to modify the urls so you break them down for seo purposes? For example you have a one page template page.html and then there are other urls created from clicking the nagigation links?
If i am correct in my assumption, you really have two questions. First is the Back button and second is SEO.
If you go with the hashbang route, (anchorts) then you neeed to tell google spider how to parse only the hash content . You can read more about it here: https://developers.google.com/webmasters/ajax-crawling/docs/getting-started
Eseentially you are mapping the hashed page to one that only shows google the content for the specific slide.
If you are going with HTML Pushstate then you have to support the full urls if they are reuested by google spider.
In my opinion using Hashbang is the cleaner and easier approach.