If this apache server is serving a webpage that is not internal, ie. you and your friends are not the only ones accessing it, then you will have to leave it at port 80. but if this does not apply to you, I recommend changing the default port since you will most likely get a little less scanned (and hence be slightly more secure) - you will need to explicitly state the new port when accessing it (eg. www.domain.com:811
) but since this is internal, you will know this....so no problem.
As for the firewall, if you are running apache...you should really ditch the default one and look into learning iptables. This way you can block off everything except what you explicitly want. BTW, what is the default firewall in MDK? I'm sure you can google for documentation to it, which should help you figure out the appropriate steps.