Help me with my campaign.

[GolemsVoice]

Since I may make the DM somewhere in the near future, I seek advice by experienced DMs on my story.
It will be a Warcraft Campaign with the WoW books, but if you don't know about the setting, feel free to make comments, too.

So, the story so far is:

The heroes (5, so far) are invited to a great Tinker's Congress, where they function as bodyguards, or, if they have a more specific background, such as, say, a paladin of the Holy Light, they travel with their order, because the rivaling Goblins and Gnomes would not trust each other's men. Here is room for various side-quests, brought to them by the various tinkers, but I can't think of an. Everytime I think about it, some WoW-MMORPG quests come to mind, and I definitely want to avoid that my game plays like the videogame.

So, after they have explored the fair a bit, a Gnome comes running, and alerts everybody that the High Tinkeress Jalinda Screwbolt has been murdered. At once, the Gnomes begin blaming the Goblins for this nefarious deed, when a Goblin messenger arrives and tells the audience that they have found Gren Steampower, chief tinker of the Goblins, dead in his chamber.

Turmoil and disorder breaks los as both side start shouting insults and threats at the other, so the Heroes, as a neutral force, ar tasked with the investigation by someone who is sensible enough.
When visiting the site of the murders, the each learn that the assasin has never enterd the rooms by normal means, that the assasination weapon was a dagger in each case, and they find a scroll with acane runes in the Goblin's chamber. A successful Spellcraft check reveals the arcane mark of Dalaran, and a second Spellcraft check reveals that the scroll contained teleportation magic.

And this is where things get thin. The heroes are sent on a mission to the Violett Citadel of Dalaran, disguised as members of the Technomagi, a profession that combines magic with science, to trace back the origin of the scroll and it's owner. The mages of Dalaran do not know of the owner of the scroll, but they remember a certain Cedric Spellblade going on a mission on the date of the murder. When the heroes stay overnight, they get attacked by an arcane servant.
Cedric hides in the lower Vaults of Dalaran, and when he is confronted, he explains that he believes science and technology is an evil, and that he and some of his followers have founded the Order of the Violett Dagger to ptotect magic from outside influences.
He refuses to submit, and he and his friend Shazeera Mageblast attack (both are Wizard/Rogue combos)

That's it, so far not a bad story, but the egdes and links need some rounding, and some combining work. I am happy for every piece of advice that you can give me, be it general tips or corrections in the flow of the story.

[Abjurer]

Don't get any more people. Or max it at six if you must.

And, uh... what level are these PCs going to be?

Also, it seems very story/roleplay-driven. I am an absolute fan of this kind of thing, and I've tried it myself a few times, but I must warn you that it is not nearly as easy as you might imagine. The PCs will never do what you think they will, and even if they do you'll find that improvising gets bloody dull after a while. Another worry is the way the story plays out. It seems that quite a lot is happening that the PCs aren't a part of. Of course, this makes for a great story, but a lot of players will be turned off by a game that starts this way, and may not get into it even when it picks up later. Again, this is your call, I'm just tossing suggestions.

[GolemsVoice]

I know the PCs well, and I also know they will be content with a roleplaying-only-world, as long as it is presented in vivid colours. They (and I am, too) are children at heart. But, of course, some battles will help to un-slow the game and provide a playground for each player`s ability as well rewards.
The players will be about level 3.