seeing how its years since we played games in that series, III and IV kinda bleed together, but they're both from the era when those games had a certain quality (for the time). (the stuff after is so different it does not bleed in). But we would think that an RP based on that setting would be a character-focused NRP.
NRP because people control factions, yet also character-oriented, as not all factions would be major forces. Some could literally start as a few (or even one) individual(s), either independent or as part of another.
The setting should be relatively easy to decide, as the system could support all sorts of stories, depending on the sort of factions brought in. however, what you would have to determine early on to make an RP based on this, is the main story to follow, and how much branching you want to it. Basically how you decide ingame which campaign to play. We'd, at least initially, recommend having a strong limit on number of factions involved. The more players, the more factions can in theory be involved, but its better to have fewer to promote more interaction.
As a turn-based game system, you can even implement "turns" into it for things like recruitment of new forces, though it can be beneficial to loosen up some elements of it (perhaps have a GM decide when a turn "cycle" is over and recruitment can once more happen, rather than force everyone to post in a specific order.
does this help your idea,
@Timemaster?