In theory - yes

Practically - https://elgg.org/discussion/view/1668440/how-big-is-your-elgg-network

Also:

http://learn.elgg.org/en/1.x/admin/performance.html?highlight=scalability#can-elgg-scale-to-x-million-users

In your CSS styles. One of these:

.fa-thumbs-up:before {color:red} //not liked

.elgg-icon-thumbs-up-alt .elgg-icon-hover {color:red} //liked

.elgg-icon-thumbs-up:hover {color:red} //hover effect

Where is it?

River page displays the 'core/river/sidebar' view in the sidebar: https://github.com/Elgg/Elgg/blob/2.0/views/default/resources/river.php#L63

In your plugin you can use elgg_extend_view() function to extend the sidebar view with your own custom view (in this case suggested friends): http://learn.elgg.org/en/2.0/guides/views.html?highlight=elgg_extend_view#extending-views

thanks juho

@ buule, You can try this one and see how it works. https://elgg.org/discussion/view/2392086/elgg-android-app