WordPress MU

i think all of these are kinda tied together:
1: allow for option in settings so that users can only have one blog per user.
2:allow for option in settings so that if a user does decide to create their 1 allotted blog, it will automatically be created as their user/nick name that they have chosen: example.com/username-as-blogtitle/
3:allow for settings so that the admin can choose to only allow users to use selected themes for their blog instead of them using whatever they want.. ie matching site theme....

1 and 2 will need a plugin. 3 is built in at SiteAdmin-->Themes, simply turn all themes off and enable special themes blog by blog at SiteAdmin->Blogs->Edit instead. All users will get only the list at SiteAdmin-->Themes.

I have a plugin that does 1, but not 2.

<?php
function ds_one_blog_only($active_signup) {
// get the array of the current user's blogs
	$blogs = get_blogs_of_user( get_current_user_id() );
// all users may be members of blog 1 so remove it from the count, could be a "Dashboard" blog as well
	if ($blogs["1"]) unset($blogs["1"]);
//if the user still has blogs, disable signup else continue with existing active_signup rules at SiteAdmin->Options
	$n = count($blogs);
	if($n == 1) {
		$active_signup = 'none';
		echo 'You have '.$n.' blog';
	} elseif($n > 1) {
		$active_signup = 'none';
		echo 'You have '.$n.' blogs';
	} else {
		$active_signup = $active_signup;
	}
	return	$active_signup; // return "all", "none", "blog" or "user"
}
add_filter('wpmu_active_signup', 'ds_one_blog_only');

?>

where to i use that php? do you know how i would go about doing number 2? and number 3 still isnt working.. i only have 1 theme activated for them to use but yet it still uses the main defaul one..

Use the New Blog Defaults plugin, and you can set it to use your new default theme for each new blog.
http://wpmudevorg.wordpress.com/project/New-Blog-Defaults