The host is going to need to either a) have access to port forwarding and know how to configure that or b) put a host on the "DMZ" of the router/firewall, this is not recommended at all unless you know what you are doing as it directly exposes the host to the internet.
I do offer hosting services for a fee for a few leagues and I'm happy to help there if interested. If networking is not the issue then. There is a bit of finessing you need to do to get the game started:
1) On the host set up your game and league selection (always keep this to a minimum, even less then you would for offline play), and create the GM for the host only, DO NOT CLICK FInish on this screen yet!
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2) Have at least one other GM log in and create their GM and have them click Finish so they are in the waiting state. Then click continue on host.
3) Immediately stop the sim and save.
4) Continue adding GMs and immediately saving, clients connecting in for the first few times may crash, this is normal, you may have to recycle the server game once or twice but eventually it will stabilize.
5) Save often you will crash a lot the first few sims for *reasons*.
Eventually you will get rolling, its frustrating but we all have to deal with it. If anyone else has tips/tricks here I'm missing please post them!