To keep your options open with an open architecture you can create a multisite Network installation with multiple Networks. This means for each separate client you would give them a new Network. The advantage of this is that you can offer the scalability to Clients and keep your options open. Clients can easily have more sites (sub-domains) added to their Network.
structure would be
Network1 > abc.com (main site for the whole WordPress Multi-Network install)
Network2 > client1.com
Network3 > client2.com
Network4 > client3.com
Network4 > client3.com/shop
this shows,
- Client1&2 have only one main site.
- Client3 has a main site “client3.com” and also one “client3.com/shop” subsite/sub-domain.
To make all this happen you need to install the plugin wp-multi-network. Follow the install guidance for setup within wp-config.php for the plugin and
also add this to your wp-config.php file..
define( 'WP_HOME', '//' . $_SERVER['HTTP_HOST'] );
define( 'WP_SITEURL', '//' . $_SERVER['HTTP_HOST'] );
Be sure when you create your WordPress Multi Network installation select “subfolder” install and not “subdomain” installation (refer to the codex codex.wordpress.org/Create_A_Network) and configure your sites for wordpress pretty permalinks (ref codex.wordpress.org/Using_Permalinks)