If you want to open this season, do it as of yesterday.
If you plan on doing a haunted house next year, do it towards the middle-end of spring and get as much of the community involved as possible.
Maybe see if you can get the local community center to donate the space for a weekend or two.
How long (dates of operation) do you intend on making this?
How extravagant do you want to be?
How much capitol do you think you will need to fund this, and have you already created a detailed breakdown of costs/fees/and other misc expenses, did you remember to leave some wiggle room in case of any last minute expenses required by your FM or BI in order to open?