The story begins with H1: Keep on the Shadow Fell. I've read the article on Eberroning it and like the suggestions.
After that is where I could use some help:
The campaign will then follow the model given in Red Hand of Doom. I like the way the story is paced and I want the characters to feel like they're resisting an invasion.
The story is going to be Red Hand of Doom but with undead. It turns out Kaleral (H1's main antagonist) was not alone and actually was but one of many in Karnath and while the heroes where successful at preventing anything from happening in their small neck of the woods...others weren't so lucky. So, now the undead armies that have successfully invaded are working their way accross the land to crush any pockets of resistance, this includes the hero's small little vale.
I think the campaign will be a cool heroic tier story arc, but I want it to also have the Eberron feel the book describes. How to bring in the dragonmarked, houses, flying ships, and pulp action?
Any advice you can give on and/or around the subject would be great. Believe me, I'm all ears.
How did the vale hear about the other places not fending off the undead? It's either going to be from a House Sivis message station, from a message carried by a House Vadalis pidgeon or something, or maybe a Lyrandar airship. As for bringing them into the game, easy: living customers are paying customers. They probably don't want too many undead running around. Maybe your party will need to convince House Jorasco that maybe they should stop charging for Remove Disease, if there is a plague coming that causes the undead. Or, maybe only the joint cooperation of House Orien and Lyrandar will be enough to bring supplies and troops to the front lines fast enough. Think about what the Houses DO, and how that could be used against a zombie invasion. I mean, I would think that rich people would start asking for House Kundarak services to fortify their homes, taking up time that could be used by the House to make the entire CITY safe. Stuff like that.
Also, make sure your characters travel. A lot. Y'know the first three Indiana Jones movies, with the scenes with the maps and the red lines? During portions of the campaign arc, the PCs should need to run around going to some of the cool places that are in the EPG. Just remember that, for the most part, travel is safe in Eberron if you're using the lightning rail or airships. Just skip to describing their new port of call. In the Seekers Eberron Module, I think you go to about 8 COMPLETELY different locations before you're level 5.
As far as pulp action goes, there is a good example in Seekers of the Ashen Crown, (should be, as it is the Eberron Module) where there is a spinning column that, if a character uses it, allows them to shift anywhere around the column (by grabbing it and holding on to it) or using it to get a running start to jump in any direction they want (by grabbing it and using momentum to 'throw' themselves).
In my games, I have a houserule that says that nearly any interaction with the environment in combat is a minor action. Standing next to a fruit stand? Minor action to take a coconut and smash it into your opponent's face. Next to a table and being attacked by ranged baddies? Minor action to knock over the table so you have cover, another minor action to send the table rolling Indiana Jones style. Bad guys under a chandalier? Minor action to try to cut the rope.
I use minor actions because a lot of the time, players are worried about the damage trade-off of standard actions to use the environment vs. damage they could have done with one of their SA powers. I found that allowing them to interact with the environment as minor actions, or sometimes free actions, makes the players more likely to use the environment to give a pulpy feel to combat.
Give little bonuses for doing cool things, like a +1 bonus to attacks against enemies lower than you while you are standing on a table, or +1 speed when using a chandalier to swing across a room, stuff like that.
My only point would be to suggest that you modify the metaplot further, call Kalarel an agent of the Emerald Claw, and have the undead hordes be a stolen Karrnathi "Risen Patriots" (undead) legion.
I may come up with more later.
Maybe the Houses will supply the resistance with Airships to fly in supplies or bombard the undead armies from above, supply the group and resistance with magic wands/potions to combat the undead, elite squads of mercenaries, guides to lead the way through dangerous terrain. As CorrinAvatan said, the houses are merchants, and undeads dont tend to care much about economy, so undeads are usually bad for business.
I'm about to start a new campaign where an early storyarc will involve House Sivis and the Korranberg Chronicle. Korranberg Chronicle is the most read "newspaper" in Khorvaire, and there are, in my view, quite a lot of bards or other 'journalists' who are dying to get featured there. So one very ambitious gnome will take upon himself to find some heroes (my players) and write about their adventures! "You can't fake a hero!" "No better story but the real deal!"
He will write more and more of them, forcing the players to adapt to a new situation in which they are getting known around for stuff they do.. how they will react will be interesting to me, but in any case, this gnome will try and start adventures for them, start horrible things to get the players involved when he feels they haven't done anything in a while, so that he can continue writing about them. The Korranberg chronicle will get more invested in this gnome as they notice an increase in revenue. And it should all lead to a final confrontation with either the gnome or the Korranberg people. Or something!
I haven't exactly planned out the details of it yet, but to me it feels very Eberron'ish. They players will be investigating a plot that turns out to be a plot of someone else which is sponsored by a plot from a third party. And the end result is the party might/might not get recognized more often and either welcomed, feared or rediculed. If they without question accept the stories, then maybe whenever they enter a new town, people will recognize them and panic because they think/fear something is afoot.
What I hope you can take from this example is to think in plots and purposes. Who started the invasions, who is the resistance, why might the Houses help the resistance? What do they want in return? What are the consequences of it? And so on, there are many angles and players in this world, and depending on what your plan is for after the heroic teir, you would do well to consider who is taking an interest in this invasion. Maybe someone, or a secret group, in the dragonmarked houses initiated the invasion to accomplish something the players won't find out until later? Or maybe use the invasion as cover to accomplish something... to me, those plots within plots are a big part of Eberron
Oppotunist people taking advantage of what happens in the world.I think the best thing you can do to create an Eberron feel is to be openminded about creative suggestions from your players. Do you disallow or make it too diffuclt to use the environment, then you wont get that cool action feel to it. If on the other hand, you're large and openhanded about it, then you'll get that feeling. Reward the players for thinking creatively
Make encounters that you will only get in Eberron; good aligned vampires, evil unicorns, air ship battles, etc.