This is partly related to this question.
I am deploying a PHP/MySQL application in my office, for my LAN. It will not be accessible to the outside world unless they can enter my wireless network (which is not broadcasting the SSID so only we know about it). This application will be hosting sensitive data that cannot be compromised. So my question is, is it safe to use an XAMPP installation with it being behind a firewall and an encrypted, invisible wifi connection, or should i take further precautions?