Adding plugins and themes into your demo platform is straight forwards in that you would upload or add them in the same way you would with any WordPress website. Where a little more attention is needed, is when you are activating plugins or enabling themes.
Within a WordPress multisite environment, you add both plugins and themes via the network admin page using the relevant menu options. Plugins -> Add New and Themes -> Add New. But once they are uploaded you may not want them to be available to all sites within your network.
For example, within network admin, when you add a new plugin, you get the option to Network Activate the plugin. If you do Network Activate a plugin, that plugin is then active for all sites in the network. Even those provisioned by Easy Plugin Demo.
It is the same for Themes. Choosing to Network Enable a theme, means that theme is available to all sites in the network.
Therefore, you should only network activate plugins and enable themes that you need to be running on all sites.
If you only want plugins and themes to be available within specific sites in your network, i.e. those provisioned by Easy Plugin Demo, then you should leave them deactivated/disabled.
If you are not using Clone templates within Easy Plugin Demo, you choose which plugins to activate and enable within the Easy Plugin Demo settings screens. Premium Pack users can also select which plugins to activate and themes to enable within each Demo template.
Enabling Plugins & Themes within Clone Templates
If you choose to create a site which you will configure as a Clone Master within Easy Plugin Demo, once you have provisioned the site, browse to its admin and from within the Plugins menu, activate the plugins you wish to have active for the clone master – and any sites provisioned from it.
For themes, it is a little different. First, within network admin, you will need to edit the site you created, click the Themes tab on the Edit Site screen, and then Enable any themes you want available for the site. You choose which theme you want to be active for the site within the site admin via the Appearance menu.