Page-Specific Rewrite Rules: Improvements?

Hello!

On one specific page (/projects/references/)in my blog I’d like to read values from the URL and work with them: cat_main, cat_sub and pid (project-id).
URL example: /projects/references/my_cat_main/my_cat_sub/my_projectid

After a lot of search, trial & error I came to this solution:

// Adding Query Vars:
function my_query_vars($vars){
    $my_vars = array('cat_main','cat_sub','pid');
	return array_merge($my_vars, $vars);
}
add_filter('query_vars', 'my_query_vars');

// Adding Rewrite Rules
function my_rewrite_rules($rules){
    $my_rule = array(
        'projects/references/(.+)/(.+)/(.+)/?' => 'index.php?pagename=projects/references&cat_main=$matches[1]&cat_sub=$matches[2]&pid=$matches[3]',
        'projects/references/(.+)/(.+)/?' => 'index.php?pagename=projects/references&cat_main=$matches[1]&cat_sub=$matches[2]',
		'projects/references/(.+)/?' => 'index.php?pagename=projects/references&cat_main=$matches[1]'
    );

    return array_merge($my_rule, $rules);
}
add_filter('page_rewrite_rules', 'my_rewrite_rules');

This work’s quite fine! *yeah*
But: I’m new to this, and so I’d like to ask YOU: Is this the way to do it? What could I improve?
For example I’m not so sure if it’s realy necessary to define 3 seperate rules?

Another question: Is there a way to call different templates for the different rules? For example a list-template for both category-rules and a seperate template for the project-view?

Thanks a lot
Mark