salesforce api add leads from form - php

Question

I am trying to add leads from my contact form to salesforce. Currently I am using this solution that passes them through what I assume is the Web-to-Lead solution they have:
if (isset($_POST['submit'])) {
$ch_register_first_name = $_POST['ch_register_first_name'];
$ch_register_last_name = $_POST['ch_register_last_name'];
$ch_register_dob = $_POST['ch_register_dob'];
$ch_register_phone = $_POST['ch_register_phone'];
$ch_register_email = $_POST['ch_register_email'];
$ch_register_street = $_POST['ch_register_street'];
$ch_register_street2 = $_POST['ch_register_street2'];
$ch_register_city = $_POST['ch_register_city'];
$ch_register_state = $_POST['ch_register_state'];
$ch_register_zip = $_POST['ch_register_zip'];
//set POST variables
$url = 'https://test.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8';
$fields = array(
'last_name'=>urlencode($ch_register_first_name),
'first_name'=>urlencode($ch_register_last_name),
'street'=>urlencode($ch_register_street),
'city'=>urlencode($ch_register_city),
'state'=>urlencode($ch_register_state),
'zip'=>urlencode($ch_register_zip),
'company'=>urlencode($company),
'description'=>urlencode($ch_register_dob),
'email'=>urlencode($ch_register_phone),
'phone'=>urlencode($ch_register_email),
'mycustomefieldid' => urlencode($ch_register_dob), // custom field
'oid' => $ch_register_salesforce_id, // insert with your id
'retURL' => urlencode('http://thank-you/'), // sending this just in case
'debug' => '1',
'debugEmail' => urlencode("email#email.com"), // your debugging email
);
//url-ify the data for the POST
foreach($fields as $key=>$value) { $fields_string .= $key.'='.$value.'&'; }
rtrim($fields_string,'&');
//open connection
$ch = curl_init();
//set the url, number of POST vars, POST data
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_POST,count($fields));
curl_setopt($ch,CURLOPT_POSTFIELDS,$fields_string);
curl_setopt($ch,CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($ch,CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch,CURLOPT_FOLLOWLOCATION, TRUE);
//execute post
$result = curl_exec($ch);
//close connection
curl_close($ch);
}
The issue by doing this (if I am correct that its using the Web-to-Lead solution) the max limit is 500 in 24hrs. Some events this form will be used at day of will have more than 500 for sure. How can I use just their API I have read about? Or should I save the locally to the database then run a batch using the Force api?