(7e) The haunting - in need of advices on some points

Hello.
I'm new to the world of call of cthulhu as a keeper and the only story I runned so far is Crimson letters from the rulebook.
I have some questions about The haunting available in the quick start guide for the 7th edition.

1. What should I do if the investigators want to inspect the house right from the start ? How could I dissuade the investigator from doing so ? And if they do, what do I do in order to maintain a good story length ?
2. Isn't it too fast to simply hint the fact that Walter Corbitt's body might be in the basement with just a quick check at the central library ? I don't want to delete the hint from the story, but I still find it might be a little too easy.
3. How could I hint that it might be interesting to check the hall of records ?
4. What am I supposed to say if the investigators find the book of Eibon in the old chapel ? (I think the best way out might be to say that it's rotten)
5. How could I use the horoscope found in the hidden room in the basement for future scenario ? (Which story should I read to understand this part of the myth, and build a future scenario ?)

And I'm wondering if the symbol made with the three Y's and the eye in the center is actually part of the myth ? I can't find which cult it belong to.

Thanks in advance for any help you could provide.