Tips for setting up a reservation site and paid WordPress profiles with SEO considerations

I want to use WordPress to create a site where visitors from all over the world can register for free or paid profiles / memberships, where those paid get more exposure on the site, their profile / ad will be displayed in prominent places on the site such as best in its category (eg, geo) and / or subcategories, sidebars, etc. I want to do it so that the paid profiles have automatic monthly or annual recurring billing through my payment processor. And when they no longer pay, their profiles (and especially the profiles / ads they have in those prominent places) will be automatically deactivated / deactivated. Therefore, they will then automatically degrade to free profiles / members.

The site should also have a reservation function where site visitors can book appointments on profile pages of paid members / profiles. So paid profiles / members can get more clients / reservations in an easy way.

Visitors to the site (they must create / have an account for this) must also be able to qualify and review the free / paid profiles / members.

But since the site will address all (or many) countries in the world, the site will also have to deal with a SEO / UI language problem:

should there be some type of configuration in WP (or perhaps multiple WP installations in perhaps different site categories, each for another country / language?) so visitors to the country / language X will be able to see the user interface in your own local language X (or maybe the language they chose as their preferred language when registering, if possible). And other visitors from another country / language AND should see the user interface in their local language Y. But not only this language problem of the user interface is important, but also the SEO. What would be the best way to do this then? What SEO considerations play a role here?

What are some ways to do this?

Is it better to do this with a more appropriate theme (premium) and then add some add-ons (premium) to that? Or a simpler theme and then get most of the features of the supplements (premium)?