Wordpress Theme Setup

New website needs to be finalised and worked on: upcourses.co which is an online courses affiliate website for another website.

UK AND US SITE
Once created correctly I need it duplicated onto a subdomain so I can have a UK focusing site and a US version of the website.
To be done in the most SEO effective way.

Maybe it is best to have the UK version on http://upcourses.co, and the US site as a totally separate site on http://us.upcourses.co or https://upcourses.co/us/ ?

We will need a small UK flag for people accessing the UK version of the site, in the header, and a US flag for someone visiting the US version of the site.

Will need an SSL certificate for each added through the hosting company.


THE TEMPLATE
The template is using the theme
Masterstudy: https://preview.themeforest.net/item/masterstudy-education-center-wordpress-theme/full_screen_preview/12170274?_ga=2.223309147.1523158203.1585689200-1520357612.1580263165

The Theme version required is:
UDEMY Affiliate Theme: https://stylemixthemes.com/masterstudy/udemy-affiliate/
Can you ensure the theme setup replicates the UDEMY affiliate theme?

It is already installed and the main pages of this theme once you are away from the homepage.
e.g the way the pages are setup from the more inner category pages: http://upcourses.co/stm_lms_course_category/game-design/

On mobile, can the first section with the call to action button be the first thing that loads (not the last as it currently is).

COURSE PAGES AND CATEGORIES
Once the pages are set up correctly, I will populate all content

SEO FRIENDLY PLUGINS
Could you help and implement all the plugins you feel could support from a page load speed as the sites will eventually be large (Image CDN plugin of any kind), Yoast, and/or anything you think could support as the site builds?