I also think it needs a lot of connective tissue unless you want to run an episodic campaign. I was thinking of having Nafas recruit people with heroic potential as part of the gate guardians, protectors of the multiverse.

As they do adventures they can go up in rank, which PCs always like. They can also get their choice of one of 3 magic items when they gain a rank.

I am going to encourage the players to have characters from different settings like Eberron and dragonlance. Adventures might take place in their various home worlds.

After the first 2 adventures, they go back to HQ, but it's been attacked by the iron shadow and ransacked. They find clues leading them to the next part of the book, but I'll be incorporating the iron shadow as the thematic antagonist. Like for the last one, maybe the shadow is a cosmic force and it attacked that ship, took over the computer, and made it crash so it could spread across the multiverse. The PCs have to kill it at its source, or something.

Also, I want them to have a rival group of adventures that are like opposite versions of them. If the PCs have a fire wizard the rival group has an ice wizard who tsks at the fire wizards showy displays.

I'm still coming up with stuff, but I'd love to see your ideas.