I think you are making things a lot harder then they need. I am running several website from my core, and I do not have remote access enabled. It is my understanding that remote access is mainly for ssh access to your core. I also have not made any other changes to the default configuration for firewall and port forwarding than the standard configuration.
I would leave apache on 80 as this port is already set up to allow incoming connections. As, for dyndns, you can always log in to their site and it will tell where the url is pointing to, ie which IP address. I believe it also determines what IP address you are accessing their site from and if you are on your network it should show the External IP. At least it does for me. This may allow you to bypass the issue jondecker76 is referring to.
My setup is as follows:
cable-->cable modem-->LinuxMCE Core--->internal LAN
Apache: No special changes to Ports, I only changed/added entries in sites-available and added symlinks into sites-enabled
I did not mess around with any port forwarding or enabled Outside access
I hope this helps.