Not to forumcrosspost, but I will add to this from an event some time ago called the NESing Exodus.
I will begin by stating that I'm saying these things from an unknowing viewpoint of an outsider. I don't know the reasons you feel you need to do this, see. I don't know if any of these things have been addressed.
The NESing Exodus happened when the whole NESing forum's interests clashed with a somewhat strict moderation of one mod (And I will infer no further pdma here) and the displeased NESers wished a freer playground, and as such migrated to another forum temporarily.
Oh, on that account: There has to be an incentive for something like a forum migration. Why do you need your own forum? Why aren't the facilities of CFC enough? If the incentive is "I think it will be fun", it is plentily valid, btw.
Anyways, the migration was meant to be permanent, but it died out quickly.
What we learned was that:
- The forum wasn't a part of any NESer's culture. People didn't really
go there as naturally as they just
went to CFC. The reason is that there are plenty of other things to do on CFC. I rarely play Civ, for instance, but there's so much stuff to explore here there's no reason to leave.
- It caused a temporary divide which was hard to smooth out afterwards. The playerbase shrunk in both ends, making it very difficult to have any NES running. In the end, it went in the favor of the more developed site. It might be easier for you because you seem to have a larger player base, but watch out.
- CFC mods actually listened to us during the whole thing, but I don't think they took us very seriously - many of the prominent NESers didn't either. I played both horses during the event.
Additionally, a forum needs fresh blood to stay alive. It's hard to maintain a playerbase in a forum that's dedicated to one sort of forum game, even a sophisticated one like IOT. CFC has the power of having a
huge user count and the Civ series drag in natural strategy/history geeks that eat this stuff up.
If you're going to go offsite, godspeed, but you ought to look at the above problems first if you haven't already.
best regards