A preliminary investigation says you are based on Drupal 7.
And as per your requirement, the task is:
■ Upgrade your website from Drupal 7 to Drupal 8 latest stable version Drupal 8.4.5.
■ Change the home page with the latest mockup.
Main Challenges based on my previous experience:
►If your website has any such module which is not available in Drupal 8.
►The current site has administrative backend using CiviCRM, which need to take care especially.
► If your site has any custom module then I have to re-write it.
Upgrade Process:
►Make a list to the core and contributed module which is enabled in Drupal 7.
►Make a checklist, which module are present in Drupal 8, Which module not found in Drupal 8 and is they need in Drupal 8 or not.
export configuration and content entities from D7 to D8.
►Install the fresh D8
►I prefer to use composer, so install composer and then install Install Migrate Tools, Install Migrate Upgrade, Install Migrate Plus module
►Enabled the required module.
► Move all type of media, pdf file from your D7 site to new D8.
►Then start migration process using composer.
►Once migration task complete, enabled all the necessary modules.
►After that upgrade the CiviCRM to the latest version matching with D8
►Correction of the theme as per D8
►Create twig file(template file) for the home page to re-create the home page as per mockup
I am ready to start working immediately. Ping me or call me if you have any queries to complete this task
Thank You