For the 1st story(the fall of house lynch) The objective i got(by choosing 1a, 2b and 3a) says for the investigators to win"they have to kill the Maniac(named monster) Walter Lynch. When and where does he come on the board? Thx in advance and sorry if this is posted somewhere else.

Then you chosen the 1A option:

- the IV Event will put Walter lynch on the board

or

-the discover of clue 1A will put walter lynch on the board

whatever goes first

Event IV does NOT place Walter Lynch, if the investigators want to win, they need to find Clue 1 which tells you to place Walter Lynch within 2 spaces of an investigator (as per FAQ).