Send activation mail from front end
I'll focus on the "sending an activation email from the front end" part of your question, since that seems to be the crux of it:

You'd have to write a very simple, custom plugin. For instant success, scaffold your plugin using the Plugin Factory. Under Plugin Components, enable Controllers.

Unzip and install your plugin.

In the Controller class, add something like the following method:

public function actionSendActivationEmail()
{

    // Get the user from the `id` URL parameter
    $user = craft()-&gt;users-&gt;getUserById(craft()-&gt;request-&gt;getParam('id'));

    if ($user) {
        // Send the activation email
        craft()-&gt;users-&gt;sendActivationEmail($user);
    }

    // Redirect back to the page we came from
    $this-&gt;redirect(craft()-&gt;request-&gt;getUrlReferrer());

}


To create a link to this controller action in your template, do something like this:

&lt;a href="{{ actionUrl('yourPluginHandle/sendActivationEmail', { id: user.id }) }}"&gt;Send activation email&lt;/a&gt;