I myself am partial to MT and PT nation RP, as anything getting too far into the future becomes hard to manage (I know this from experience). Currently I'm setting up an ancient Greek setting region with some fantasy mixed in, as well as building a dice warfare system that may help here if anyone is interested in it.
From my experience in running RP regions over the last year or so I have learned a lot through trial and error. The best thing to start with before starting RP is to figure out RP rules, as well as figuring out if you want a standardized population amount increasing each year or individual nation growth. I can also recommend that we need RP moderators, as an RP without moderation quickly devolves into a horrible RP with god-modding among other things. Oh, and if we do nation RP a world map is a must.