Help finding the best way to translate my website

I will start by saying I'm a total noob when it comes to Wordpress, so sorry if this sounds like a dumb question. I managed to built a website by myself and I've learnt a lot in the process, but there are still lots of things I still don't fully grasp.

I basically built a simple website to offer my translation services. I'm Spanish, I built the website in English and now I want to translate it into Spanish. I obviously can do the translations myself, so I would like to avoid paying a yearly fee for plugins that offer automatic translation like WPML or Polylang.

I see the TranslatePress plugin allows you to translate a website for free into one language, but you don't get any SEO support. Is there a workaround that will allow me to translate the website myself and then add the Hreflang thingies and work on the SEO in English and Spanish by using a free SEO plugin? As a freelancer it's important that the Spanish version will also rank well on Google, so people can hire me.

The concept I don't understand well is slugs. I think with TranslatePress I could have a www.example.com website and a www.example.com/es/ website, but the different sections of the website would still be in English (e.g.: /es/about-me instead of /es/sobre-mi). Am I right?

Any help will be so appreciated. I've been working on this in my free time for two months and I can't see the light at the end of the tunnel yet.