Well then we must discuss what's the plan. It's pretty easy about Lance, true, but we need to find what to do about others as well...I'll write what I can think of.

I'd like it if it starts off as only Renais versus Irea, to be honest. Then everything would go on in succession, all the events. 

Lance would leave Irea to go towards Grado first, seeking an alliance. You will have characters in Grado, or so I hope, so we could meet there eventually. They would head over to the free city next, but by that time Renais will have contacted Hiactance and, revealing the new alliance, Hiactance will attack the group. They would make their way through this new enemy territory in order to reach the free city and find new allies. By this time, they're next destination would probably be the far away Jehanna. This would unfold over a long period of time, of course, and with many Fire Emblem signatures encounters such as bandits and what not.

As far as the mercenaries go...we could indeed still wait for them, since they would not have much to do before Lance gets over there. Maybe they can partake in hostilities between North and South Carcino? This way we could use our Carcino characters, who have yet to be made, to roleplay together to some other part of the story. 

As for Renais king...maybe this part would be more about political intrigue? I know we talking fire emblem here, but it's also a roleplay so maybe? Maybe intrigues happen between Frelia and Renais, and from the inside their trusts towards one another falter. Something like that ?