I would create a child theme based on Adaptable. https://docs.moodle.org/dev/Creating_a_theme_based_on_boost
Within your child theme you will be able to create a layout (in the layout folder) as below - my theme is called ld35:
Then in your theme's config.php file make this the frontpage layout:
$THEME->layouts = [
// The site home page.
'frontpage' => array(
'file' => 'frontpage.php',
'regions' => array('side-pre', 'side-post'),
'defaultregion' => 'side-pre',
'options' => array('nonavbar' => false),
),
Hope this makes sense,
Dave