Well, EQEmu does an amazing job in emulating Everquest but personally I wouldn't recomment or use it as the code base for a brand new project.
I'm pretty sure you know and already discussed the Worldforge Project but just in case you don't I would recommend that you check it out.
http://worldforge.org/
As long as you don't sell or give away(e.g. binaries) anything that has parts that are licensed under the GPL or certain other open source licenses you can do anything you want. If you do, you have to provide the source.
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