Re: Install was successful but….
No-one knows anything about writing plugins when they start writing them. You said you were learning PHP, this is your chance to put it into practice/get better. This might not work but it’s the basic way you’d go about it I think.
add_action('register_user', 'myfunctiontochangeuserstatuswhentheyregisterheh');
function myfunctiontochangeuserstatuswhentheyregisterheh( $user_id ) {
//I suspect somethin' like this:
$user = get_user( $user_id );
$user->set_role('inactive');
}