Moss said:
I'm thinking my storyline might be a little too well thought out though
It's a good idea for a story, but you've plotted it too much. You'll end up either railroading the players. The other problem is exposition, from the sound of it they're getting infodumps at regular intervals, which is horrible to the game flow.
Rather than dreams, a better idea may be to have the sorcerer somehow related to all of the characters, and after his death the characters are nominated to receive his legacy, perhaps as a will or perhaps they are asked to identify his body. You can then have them given the journal as one of his possessions. You don't have to abandon the dream route either though as it could be a useful mechanism, if any of the characters are magically sensitive themselves (or in a pinch, the sorcerer cast a spell on his journal which would affect the first character to read it) they could begin reliving his last few days. Don't give too much away through this however, perhaps the character would get the feeling that something is important, but not know why unless they put two and two together themselves.
To future proof, perhaps have the circumstances of his death noted in a police report too, it could be useful to spur the players on later. If the guy was stabbed to death by a funny shaped knife in a sealed room then having an assailant wielding an identical knife materialise in a characters room and attempt to murder them is an easy way of putting them on track if they're lax in their investigation. Naturally, the attack would be smoothed over by the corrupt cops, but if they need another prod down the line then they could be hauled in for questioning regarding the homicide and threatened with imprisonment if they continue investigating .... and so forth. Don't worry about this kind of stuff too much, the players may or may not go down any particular route. The more doors you can leave open for yourself the easier it is for you to deal with what the players decide to do.
You need to flesh out the cult too. Like I said, the more you understand the nature of the villain, the more natural you can make the game flow. They're bringing in monsters, but why? Consider the following:
They're paid to bring in these "packages" by another figure. This means they're criminals rather than cultists, and as with organised crime everywhere then some city officials are in their pocket. It changes the nature of the threat too, if the players become a thorn in their side then the response is likely to be underworld thugs, paid hitmen and intimidation. Do they know the nature of the trafficking they're involved in? If so then perhaps the head of the crime family is the only true cultist. If not, perhaps the players can find evidence to prove the gang is being used, and convince them to team up to thwart the plans of the cult.
They're bringing them in for power. The creatures are part of a ritual or similar designed to increase the magical power of the cult. That being the case, the players may face mystical as well as physical obstacles. In addition, where do the officials stand? Are the city officials secretly corrupt sorcerers who use their position to hide the unspeakable evils at the rotten core of city government, or are they simply allies who were swayed by promises of unimaginable power? If the former then perhaps the city cannot be redeemed, if the latter then maybe the players can instigate a revolt, or blackmail one of the cult's allies into helping.
There's a host of other options there too, like I said the more you understand who the cult are and what they are trying to do the easier it will be for you to shape the game, and judge how the cult would react to the meddling of the players. It also helps to establish other strands you can use to weave the characters in, if for example you went with the first option then perhaps players familiar with the criminal fraternity might hear rumours about a small time gang who appear to have gained in power rather quickly, or maybe one will be invited to assist in a "delivery".
Basically, you're thinking too much in terms of story and not enough in terms of character. The story is written as a collaborative effort during the game, not by the GM beforehand
Come up with a well fleshed out foil for the players to face and let them dictate what actually happens. Maybe they'll discover the chief of police is corrupt, maybe not. It doesn't hurt to have these ideas floating around, but don't try to screw it down too much. To give one problem with your plot thus far, at several points you say the players could leave town, but nothing after that. If the cult see them as a threat is it really as easy as just quitting town? What if this is your first play session, do they spend the next three twiddling their thumbs? Figure out how the cult would react to it and instead you can fill those three with a daring flight across the wilderness pursued by raving madmen and slobbering things of unpronounceable names instead.
In short, don't try to plot it all out beforehand. You'll need a hook or two to get the players involved in the investigation, and you need to know what the cult plan to do and what will happen if they're not stopped, but everything else depends on the actions of the characters. As long as you have a rough idea of where you want the story to go so you can nudge them one way or the other that should be enough.
I should point out that due to the nature of the game most of the players won't be trained soldiers. Player classes don't really feature in CT and unless you're playing a combat focused campaign characters aren't going to prepared for big fights. Most of the players will be civilians of one kind or another, they'll still be able to point and shoot a handgun, but they're not going to have combat training and they won't have access to automatic weapons and armour.
Key thing to remember in any setting where there's a force for law and order is carrying weapons all the time and killing people out of hand tends to have consequences, and that applies to both the players and their opponents. Personally I never kill a character unless the player is being monumentally stupid or has screwed up somehow. You don't have to have them killed, maybe they just get roughed up instead, or knocked out and captured. And to paraphrase the old CoC rulebook, even when KO'd by a monster they may still awake to find only their left forefinger missing, for who can predict the actions of something man cannot comprehend ...