[4E] Eberron War

[Duos Greanleef]

I DM a group of four level 7 PCs and we've been in Eberron lately.
Story if you care about it:

Spoiler

Show

We started two sessions ago being teleported by the lone arcanist of Greenheart to a random circle in the middle of an abandoned tower in the Shadowcrags. From where they are, they can see The Lake of Fire.
Back up: They were sent into the Demon Wastes by The Great Druid Oalian to find out why the gnolls have been acting up all over the continent.
Ok. So they drew some lines and between knowing that gnolls are fiendishly involved, constantly active volcanoes are generally a place for evil folks to hang out, and the fact that It's the only landmark they have to go by; they're heading that direction.

My idea was that some huge, indigenous tiefling/human/orc/half-orc tribe has been asking Yeenoghu for help. He sent a bunch of gnolls to do so, but they're not really helping the tribe so much as they are killing whatever they want.
Now the tribe has realized that they're in over their heads and they want out.
The idea is to capture the PCs, parley with the chief and eventually help the tribe stem the flow of gnolls. Now there's already a small army of gnolls and a tribe large enough to constitute a small army.
The PCs are going to be the deciding factor. If they agree to help the tribe and successfully kill enough gnolls, then Khorvaire is safe for now, and they are heroes of the Demon Wastes and unsung heroes of the Continent.
If they decide to not help, or they fail: The continent could potentially be overrun with Gnolls by mid-Paragon tier. {Which would be a whole 'nother brand of awesomesauce on its own}

The Questions:
Does this sound feasible enough to you?
How do you run a huge fight (Like a couple thousand people on the field) in 4E?
Please help and thank you in advance.

[Mando Knight]

The Questions:
Does this sound feasible enough to you?
How do you run a huge fight (Like a couple thousand people on the field) in 4E?
Please help and thank you in advance.

Feasible enough, but remember the dos and don'ts of running large fights in RPGs:

Don't run the fight straight-up with everyone on the map. Takes too long, and gets boring.
Do highlight the players' roles in the conflict, cutting out all of the creatures except the ones immediately dealing with the PCs.
Don't simply put the PCs on the front line. It turns into another wave attack encounter without much maneuvering room.
Do give the PCs Spec Ops roles in the fight, having them take down key targets that could make or break the battle.

[Yakk]

If there is a fight in which the PCs don't matter (ie, 100s or 1000s of beings on the same scale of power as the PCs), then you shouldn't be running it. You could run short vingettes with far fewer numbers involving just the PC local area at best.

If you are in a fight where the PCs are a significant force (late-paragon PCs, a human army, against an army of demonic gnolls), you can use swarm rules to represent large forces of lower power level opponents.