Hi, I will not have all the answers you seek but I can help with some of them.
I do not believe you need to contact anybody to make a wiki page for your nation, as I remember I just made an account and later I could edit or create pages. On the top right corner there's a login link, maybe you'll need to be approved, but you will certainly need to create an account so go ahead.
Map factors are best requested in the
worldbuilding - Planning Room section (link), geography is left to the super-geography-god Oz who will tuck you in our world in the
Official map thread (link). Our map and placement rules are very strict so to keep a "realistic" approach to what we call worldbuilding. Here's some
policy for large nations (link) and here's a wiki help for
worldbuilding / RP planning (link).
That said, I can try to guide your 1st steps to your nation building. It is correct Taijitu world is earth-like, but it has slightly less population than "Earth", roughly two thirds, so if you have a country like France it'd have around 40 million people, yet we do not encourage large nations or you'll have to RP - kinda explain - how your nation is "presently" large. We keep our map mostly clean to accommodate different RP approaches and new nations. Custom maps will face the mighty opposition of changing Taijitu world, which most "elite" RPs dislike, but who knows, make your case and
the Cabal might treat you well. You may "not care" for taijitu map if you wish, just make sure it doesn't conflict with the worldbuilding. There are also other sections of our RP dedicated to less realistic sets, such as sci-fi and fantasy.
You don't need to follow anything from NationStates and using it's stats is discouraged, we have a lot of old players that have nations with tens of billions of inhabitants, they do not fit in our worldbuilding.
ah...I shouldn't write this much...hopefully Khem or Oz might help you further, we also have IRC channel that we may help you discussing your nation, many RPs started there. Well, have fun!