WP Multisite: Setup, migration and safe backup

I have a WP single install site at MYSITE.com/subdomain1/website1

I want to create a WP Multisite at MYSITE.com

After creating the WP Multisite MYSITE.com I want to migrate MYSITE.com/subdomain1/website1 to the WP Multisite including all of its plugins, Membership (plugin) data, databases etc.

1) Please give the clear step by step method to do this
2) Please give the steps to backup the single user site described above

Thanks in advance