This is a pretty good start, but I always believe you should do requires like this..
PHP Code:
if (!require("config.php"){
//Return: Your config is missing!
}
if (!require("classes/users.php"){
//Return: Your users class is missing!
}
if (!require("classes/core.php"){
//Return: Your core class is missing!
}
if (!require("classes/safety.php"){
//Return: Your safety class is missing!
}
For all you people that don't know PHP that well, That checks if it's there, if so then require it, else return an error