You may use a plugin for slider but you will have to add the shortcode in the php file of slider and hide the original slider of this theme using css.
you may include a video section using elementor before the footer position. it also requires adding the_content() function in the home template.
could you please share your website link along with your wordpress log in details on [email protected] so we could check and fix it, please also explain the issue as well.
You wont be able to use elementor to customize our front page template. although you may use it in the front page to add templates and its widgets on the bottom.
and you may add pages using elementor.