Well, why is the login server on port 8080?
If you're looking for security through obscurity, 8080, and eAthena itself, aren't obscure.
If 6900(the default) is blocked, then it is likely 6121 and 5121(map) are blocked as well.
Multiple IPs doesn't mean no firewall(shouldn't, anyway) so it may still be a port forwarding(or more likely, port opening) issue, unless the proposed eAthena server is DMZed.
Finally, the char_athena.conf file has to be set to make the char server aware of the login server. By default it's told to look for port 6900.
Same goes for the map server.
Don't be an eAthena
, if you can figure out Linux(not saying its necessarily hard) you can figure out the conversion from the Windows install directions to the Linux install directions except for this: Being a direct-web server, set it up with the proper IPs according to the LAN versions(swap out the external IP for the internal) of the guides, unless you want to connect from the LAN as well(eAthena is kinda picky about that kinda thing....)