As I understand your question, you are only allowing the ports you mentioned. I therefore assume you have everything locked down and are only allowing data from those ports to be let in. If this is correct, then you are certainly on your way to secure your system. However security does not stop there. A very large portion of hacking occurs from inside the organization.
Attacks come in different flavors and methods.
One for instance is virus attacks in the form of e-mail attachments. Based on your email, you are allowing FTP communications. Many people forget to not allow anonymous logons, therefore allowing anyone to gain access to the FTP server. Become an expert and answer questions targeted towards a specific category. Become an Expert for this site.