I just got the core set and was looking through the cards, and I think I'd like to try a Hastur deck, based around forcing things insane and keeping them insane. Here is the list of stuff I've come up with so far. Does anyone have any advice?

3 x Apeirophobia
3 x Bearer of the Yellow Sign
3 x Deranged Sailor
3 x Erich Zann, Strange Virtuoso
3 x Final Note
3 x Guardian Beast, Servant of Serapis
3 x Hastur, Lord of Carcosa
3 x Horrifying Daydreams
3 x Lost to the Madness
3 x Messenger from Beyond
3 x Power Drain
3 x Scotophobia
3 x Sedated
3 x Shadow Eater
3 x The Guzheng, Item of Ill Fortune
3 x Thing from the Stars
3 x Victoria Glasser, The Society Hostess
3 x Victoria's Loft
3 x Victoria's Protege

Now I know it's too many cards at the moment, but the idea is there. I'm looking to get (and keep) Victoria's Loft out to keep their people insane. There are several cards that remove Terror icons and Willpower, so I can hit as many things as possible.

What would you add/remove?

I'm not an experienced player, but after playing Hastur quite a bit lately I'll offer up some suggestions:

You've got too much redundancy focused on driving characters insane. Even with Hastur (which will take a while to get out as you don't have any cost reducers), you will have a difficult time facing down other Mythos decks that are protected from terror and have direct damage capabilities (namely Cthulhu, but also Yog and Shub to a lesser extent), and you would be hard-pressed to deal with Ancient-Ones. I think a good Agency combat deck with plenty of Willpower could also rush to a victory. And Miskatonic just got a bump with their new relic that provides both Willpower and Invulnerability.

To make this viable, you need a second route to victory, or an alternate method of controlling/damaging/harassing your opponent. Granted, Hastur does have a lot of great cards to drive your opponent's characters insane, but it also has some nice discarding effects, as well as the ability to steal characters. Personally, I think the most effective combo would pair up the "drive insane" mechanic with character theft. This means including a must-have card like Infernal Obsession, as well as Blind Submission and possibly Harbinger of Insanity.

I've also found that characters are the heart and soul of a deck, and you should aim for close to 30 (you can include fewer depending on the deck, but 30 is a good number). Of course, having this many characters will eat into your Event and Support cards, so look for combos between your characters' triggered abilities to take the place of including too many Events.

Right now you've got 27 characters, but most of them cost 3+ (you have 9 that are 2-cost, and zero 1-cost). This means your deck may be slow to develop. The Dangerous Lunatic is a 2-cost character that combos perfectly with your theme, so I would take a look at him. I would also consider the Demon Lover (another 2-cost character), and throw in the Harbinger of Insanity as well as some low-cost Cultists like Performance Artist, Wandering Inmate or perhaps Renowned Sculptor (+ the Scalpel to take away terror icons). Add Sirens of Hell to all of this and you've got multiple ways to take away terror icons, steal opposing characters with skill up to 4, and destroy characters that are insane (even Ancient-Ones). Note that Dangerous Lunatic and Victoria's Loft don't play nicely together, so you'll have to choose one or the other. I've found uses for both, but I like the flexibility that Demon Lover and Dangerous Lunatic provide during the story phase.

Cards you've got listed that I thought were nice but I ultimately weeded out of my deck:

Erich Zann, Sedated, and Power Drain (that last one was tough, but I never seemed to have a 2-resource domain undrained when it counted most). You could also cut Final Note because you might not reliably succeed at story (as that's not your deck's primary focus). Last, I would check out the Stygian Eye from Into Tartarus. I think it might prove more useful than The Guzheng.

That's all I've got for now, hope it helped!

A quick follow-up: Check out a card called Spawn of the Sleeper.

With some crafty use of the Messenger from Beyond + the Scalpel, you could permanently steal an Ancient-One from your opponent (or any character, but stealing something like Cthulhu would be pretty funny). And unlike Infernal Obsession, Spawn of the Sleeper isn't an attachment, so it's not easy to undo.

Also, Messenger from Beyond + Scalpel + Old Man of the Woods should be able to take care of any problem characters.

I have a similar deck, but I try to mix in some character destruction along with insanity. Scotophobia will help remove terror icons to make things go insane. Sirens of the Deep (?) will destroy a character when it goes insane. Granny Orne will destroy insane characters. I would consider some of those as well. I will post a deck list sometime tonight (hopefully, got some football to watch) to show some mods I would make.

Well, if you add in some Shub also, you could play one of my all time favourite CoC insanitycombos:

Play Victoria, and make one character insane.
Shocking Transform Victoria to play Hungry Dark Young.
Resurrect Victoria with HDY and make another character insane.

Simple, yet effective, and this simple combo base can open up a whole new bag of shenanigans upon your opponent!

Nice one, I like it