Optimizing mod_rewrite

Question 1

Any sort of optimization will require a "blank" check in your php scripts, because paths that aren't there will still have a $_GET[''] variable associated with it, just that it'll be blank.

As far as the "state" and "national" URLs go, there's pretty much only one thing you can do, combine these two rules:

RewriteRule ^state/([A-Za-z]+)/?$ index.php?r=$1 [L,NC]
RewriteRule ^state/([A-Za-z]+)/([0-9]+)/?$ index.php?r=$1&class=$2 [L,NC]

by making the "class" optional (but there will still be a "class" parameter, it'll just be blank):

RewriteRule ^state/([A-Za-z]+)(?:/([0-9]+)|)/?$ index.php?r=$1&class=$2 [L,NC]

Same with the national:

RewriteRule ^national/([A-Za-z]+)/?$ index.php?r=national&show=$1 [L,NC]
RewriteRule ^national/([A-Za-z]+)/([0-9]+)/?$ index.php?r=national&show=$1&class=$2 [L,NC]

gets combined into:

RewriteRule ^national/([A-Za-z]+)(?:/([0-9]+)|)/?$ index.php?r=national&show=$1&class=$2 [L,NC]

But the school stuff is a little more complex. You can combine some of them, like:

RewriteRule ^schools/([A-Za-z-]+)/?$ index.php?school=$1 [L,NC]
RewriteRule ^schools/([A-Za-z-]+)/([A-Za-z]+)/?$ index.php?school=$1&show=$2 [L,NC]
RewriteRule ^schools/([A-Za-z-]+)/([A-Za-z]+)/([A-Za-z]+)/?$ index.php?school=$1&show=$2&sub=$3 [L,NC]

can be combined into just a single:

RewriteRule ^schools/([A-Za-z-]+)(?:/([A-Za-z]+)|)(?:/([A-Za-z]+)|)/?$ index.php?school=$1&show=$2&sub=$3 [L,NC]

while the

RewriteRule ^schools/([0-9]+)/?$ index.php?r=schools&class=$1 [L,NC]
RewriteRule ^schools/([A-Za-z-]+)/([0-9]+)/?$ index.php?school=$1&class=$2 [L,NC]
RewriteRule ^schools/([A-Za-z-]+)/([A-Za-z]+)/([0-9]+)/?$ index.php?school=$1&show=$2&class=$3 [L,NC]
RewriteRule ^schools/([A-Za-z-]+)/([A-Za-z]+)/([A-Za-z]+)/([0-9]+)/?$ index.php?school=$1&show=$2&sub=$3&class=$4 [L,NC]

can be combined into a single:

RewriteRule ^schools/([A-Za-z-]+)(?:/([A-Za-z]+)|)(?:/([A-Za-z]+)|)/([0-9]+)/?$ index.php?school=$1&show=$2&sub=$3&class=$4 [L,NC]

Question 2

You can create a big regex for each 3 pages, but you'll have to test it if that actually makes things faster or slower. If Apache has to apply more regex before it can serve a page, it will be slower, but if it has to apply a complex regex to the url, that might be slower than applying several simple regexes to the same url. Mod_rewrite is definitelly faster for url-rewriting than most programming languages are, mostly because to rewrite an url, you don't need to load any interpreter/compiler.

If you are able to use the END flag instead of the L flag, this speeds up rewriting a bit, because unlike the L flag, the END flag will stop rewriting completely, not just this 'round' of rewriting. It is however not available on old versions of Apache.

However, you are redirecting all your requests to index.php, so having a rule like:

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^ /index.php [L]

Then check $_SERVER['REQUEST_URI'], for example like this:

$boom = explode( '/', $_SERVER['REQUEST_URI'] );
#var_dump( $boom ); //Something like Array( '', 'state', '2011' );
if( isset( $boom[1] ) ) {
  if( $boom[1] == 'state' ) {
    if( isset( $boom[3] ) ) {
      $r = $boom[2];
      $class = $boom[3];
    } else if( isset( $boom[2] ) && intval( $boom[2], 10 ) == $boom[2] ) {
      $r = 'state';
      $class = $boom[2];
    } else if( isset( $boom[2] ) ) {
      $r = $boom[2];
    } else {
      $r = 'state';
    }
  } else if( $boom[1] == 'schools' ) {
    echo 'a';
  }
} else {
  header( '404: What the heck is this?!' );
  //No, don't use this header... 
}