My votes are as follows:
Higher-than-usual volcanism, because I /like/ cliffs and magma.
Mineral scarcity somewhere in the middle btween the default and the maximum mineral density.
Waiting for the new release to come out, because otherwise we'll be left with only a tiny handful of people doing this while everyone else runs off and finds new and exciting ways to lose.
I'm not particularly interested in display cases or temp-sensitive materials - I fully intend for my fort to go down in a fiery blaze, with wreckage all over to speak of the havoc that resulted, so there'll be rubble strewn about anyway, even if it means deliberately letting in a siege at the end of my turn.
Common rules I'd suggest: no hacking, unless it's for a magma blot for one of the previously-mentioned temp-sensitive cases. I, personally, see no need to do the DFMode swap-and-escape abandon - the mysterious wreckage is part of the nature of DF - but I won't go so far as demanding no one does it. Turns should be kept to one week, to ensure that things keep rolling smoothly while giving enough time to potentially Get Stuff Done. We should keep a list of save files in the opening post, so people can pick any one of them up and experience the world from that point as an adventurer - and, if someone finds a truly lovely site that someone else has _got_ to play, it'll be available via access to an earlier save.
I'd also like to suggest that participants get dorfed in each fort, with the traditional chronicle of how we all lived and hilariously died.