The RP I'll be making will not be on a canon continent, is the plan.

Right now I've settled that the premise will be a direct war between two large nations, that has been going for at least 2 months. Players can make a character who fights on either side either as their soldier, mercenary or some other.

The plan is that I'll update for fights on either front, in the beginning, there'll be small skirmishes between factions in separate areas to get to know one another (some players will fight other players in certain skirmishes and fronts), and eventually we reach the beginning of the meat of the plot when both factions' players will fight in a large all-out attack. Twist happens, and every player will fight side by side to overcome a new threat.

Lords will be NPC only too, to ensure existential errors don't occur. There will also be that you're forbidden from starting the RP with relationships to major characters one way or another. Your importance to them and vice versa must be earned (to ensure people don't join to make a hyped up character only to leave early).

I want it to be able to stand on it's own as a story as well, so I'm spending time writing the plot, and then make a world that will suit it. If I am stuck there, I will try and approach vice versa.

Yes I've thought through the counter-measures quite a bit. Death will be a normal occurrence too, to cull the weak.