All you need to do is to help me by making maps. So i know this is not easy job actually this is really HARD job and i know that it will be hard to find some person that will help. So mapping skills and decorating is all you need, no worries all the script will be done by ME (and maybe little help from Frictional Games Forum 'cause this is really old project and i started this when i had 0 skills, but now i improved and i wanna finish it).

Sorry for wasting your time, feel free to leave this thread when ever you want.

-This will be one of 'better' mods, (yes MODS by writing that i mean it is Total Isolated Full Conversion Mod that will be MAYBE one of the greatest), so it would be really nice to join me i would really appreciate that kinda help.
-User-s that help me will get +Reputation (if they are registered at this site).
-It would be really bad that one of mods gone into dust :/
-Guess we can do something good helping each other, i am in trouble here because i don't know mapping and decorating so i am asking YOU to help me to get out of here and together we can finish this mod :)
-You will be in credits.

I am not sure, but i think most of peoples will read this 'cause it is about money. I am terrible sorry but you won't be paid if you help me with this mod. At the end it is not everything about money right ?

Scary Atmosphere
If you're making a scary game, honestly that's not a bonus; that's an expected feature and failing to provide that will keep people from getting immersed/enjoying your custom story. Good on you for realizing it's a thing that makes games good though!
So how do scary?
Study other games that people find scary*: Amnesia TDD, Five Nights at Freddies, Outlast, Alien Isolation, Silent Hill, the beginning of the first Bioshock, etcetera. Not everyone finds the same things scary, so knowing what kinds of things could scare the pants off a large population of people is probably a good place to start.
On that tangent, some examples:
FNaF: people are scared because they know what's coming; it's tension more than just "oh my god Imma cry that's so scary"; the game trains you to expect punishment (jumpscares) if you make a mistake.
Bioshock: this is more of a personal one in terms of being scared, but most of the people I talked to agree that it is heavily atmospheric. The whole place feels alive and hostile; you have figures skittering around in the dark, psychotic people threatening to cause you physical harm, you're basically defenseless and in a strange place, being forced to move out of your comfort zone continuously or fear quit.

Boom, scary atmosphere mystery partly solved for you. Note that part of it relies on mapping, yes, you are going to have to map some scary stuff. Get good at mapping it's almost 75% of a basic CS, it's not as hard as people make it sound just go read through the screenshot criticism thread. That's what I did and there are people that think I'm damn good at it. I think they're all being too nice to me.

Long Gameplay
Repeat this mantra with me:
Long game does not mean good game
LoNg GaMe DoEs NoT mEaN gOoD gAmE
LoNg GaME DOEs NOT MEAN GOOD GAME
LONGGAMEDOESNOTMEANGOODGAME!
LONGGAMEDOESNOTMEANGOODGAME

Case and point: Dragon Age Origins
It's a good game, except the whole mage circle quest, which you can mod out because it's so lengthy and annoying. Just because my dentist takes an hour to pull out a tooth doesn't mean I'm enjoying the experience or he's doing a good job. My advice? Start small and manageable. Take a guess at what you could complete with your current skill set in two months, then divide your guess by half. This little thing is what you should be aiming to complete.

Custom Monsters
You're asking for help with maps and said you started off with no knowledge of scripting. Don't make promises you can't deliver on. Requests for custom monsters are laughed at on these forums - especially before you have at least an alpha of your game made.
"But I can't make the game without my custom mo-" shut up, yes you can, use grunts for now and use your imagination. This way the future modeller/animator knows exactly what they need their monster to do.

A WHOLE NEW WOOOOORLD
Again with the scope. Unless you have experience, don't shoot for the stars. You will crash and burn horribly. Try landing on the moon first - or better yet, circumnavigating the world.

Creepy Castles
Two things:
- you're asking for a mapper; unless you get one, you can't guarantee this
- the whole creepy thing is atmosphere

X-TREME PUZZLES
So, you want your game to be so hard that people have to stop and look up a guide in the middle? That ruins your efforts to immerse the player with atmosphere, frustrates a lot more, and worst case scenario is you alienate half of your potential audience because you wanted your game to seem smart. If you insist on having these beta test, beta test, and beta test. Whoever makes the puzzle is going to be the worst judge of its difficulty (see: university midterms).

Weird Things
I... What? The fact you're advertising weird things is a weird thing of its own! Moving on

Good Story
Two things:
- have someone other than yourself read your story and make sure it's someone willing to criticize it helpfully; a partially deaf grandmother would not count because she's too nice and can't hear half your story anyways
- make sure your story ties in with your gameplay. Otherwise, it could be the best story ever but it'll get mangled and disjointed and ignored

Custom Lantern
Same issue with the monsters.

Full Conversion
Unless you're A: Doing some fancy-ass scripting ala Palistov, B: Implementing a custom lantern that the story could not survive without because Daniel's model is just too weird, or C: Really really craving a custom menu screen
You don't need to make your CS an FC doing so just causes more headaches than necessary and increases the scope of your project

1. I have certain custom static objects (made with Blender in my maps, I can put them into the folder with my map so don't worry about that.
2. If I'm allowed put easter eggs if you will in my map (that a normal player won't notice) I'll be a VERY happy person!