Hola,
I assume your blog is a wordpress.org and not a wordpress.com one.
If so, install the WPML plugin, which (copying and pasting from its website) l_ets you do SEO for each language separately. You can set SEO attributes for the homepage, internal pages and categories for each language. Translations appear in their unique URLs and you can even put different languages in completely different domains. WPML follows Google Webmasters’ specifications for multilingual sites to the letter, letting your sites rank high on local search results. Of course, WPML is fully compatible with SEO plugins._
It will create a /en/ subfolder for the language you're translating your blog to, which seems to be your preferred solution (in other cases, i.e. a WooCommerce based on WP, it may be better using the domain option WPML offers too).
With WPML you will be able to translate everything, not just your posts (template, plugins et al).
The URL structure will mirror the main language one, but translated to English. So if you have something like www.myblog.com/seo/como-hacer-link-building, the English version will be: www.myblog.com/en/seo/how-to-do-link-building.
It also automatically implement the hreflang annotations (so you don't have to think about them).
It is compatible with WordPress SEO by Yoast, so every translated page/post can be finely optimized.
Honestly, even though the answer here above are correct (apart the "English post" category one, which is not really the ideal solution), I warmly suggest you to use WPML.