Whats great about the IV series of PbP games -in that everyone I have ever hosted- is that you are given free reign to do whatever you like. Ultimately, the game is best played with a large playground because of this. If you guys want to push it up to an entire globe, I can easily build that in Photoshop as well.
Its up to you guys
A globe sounds much better as long as its large and easily detailed. I however must say we all should start on the same continent, not necessarily close, but we should not be too isolated, though Island nations are possible for those who make them.
I definitely need a Land locked large Mountain range, black, with a lake nearby surrounded by swamp land, and a forest around the mountains, and some plains surrounding the forest with one place that is not forested, with a river called the Styx that goes in front of the largest mountain like a moat, since my main city will be built into the base of the mountain. these land also look decrepit and depressing, full of pestilence.