With apologies...
I am taking an extended break from DMing PbPs for the foreseeable future. If anyone wants to step in to the DM's chair for this campaign, you may do so with my blessing. Some notes on the plot appear below.
[sblock=The Fifth City Plot Notes]This campaign was intended to follow the episodic structure of Babylon 5 very closely, with each episode adapted to an adventure. As such, level advancement was intended to be very slow, with the first three episodes giving the PCs enough XP to level, and then each episode there-after providing 3000 XP per episode.
Because it is so closely adapted from Babylon 5, intimate familiarity with the show would be needed if the new DM intends to stay the original course. Below are some of the B5 elements, translated to 5E D&Disms...
The First Ones = celestials, elementals, and fiends. Most of the First Ones have left the mortal world to dwell on the planes, with only a handful remaining behind.
The Shadows = Rakshasa, who have corrupted some clans of gnomes, dwarves, and members of the elven warrior caste in to Svirfneblin, Duergar, and true Drow, respectively.
The Vorlons = Aasimar (referred to as Deva in this setting).
Soul Hunters = Aboleth (with enslaved humanoids being their agents as they rarely allow themselves to be seen).
Lord Clarion = Commander Sinclair. It was my intent to keep JMS' original plan for this character (i.e. having all the story points of the original Sinclair plus Sheridan) and postponing the time travel adventure involving B4 and Sinclair's revelation as the elven prophet Valen for the end of the campaign. However, I had also intended for those story points to gradually shift to the PCs, with a PC potentially taking on the mantle of Valen instead, depending on PC choices.
I had also intended to expand the role of the Wind Swords (renegade elven warrior caste faction) and Deathwalker (a hobgoblin necromancer and villain of the Goblin War, now being harbored by the Wind Swords).
Obviously, this campaign could be taken in an entirely different direction if the new DM desires, especially if they aren't that familiar with B5.[/sblock]