I know the feeling. In 2014 we put the house on the market right in the middle of the season. This meant I could not decorate for the holiday. (the realtor said something about how dead things on the lawn might scare off buyers.) Since the house has not yet sold I am still on hold with new projects waiting to move.
For simplicity sake I might suggest a roller coaster type set up. Just a short run up then a fairly gentle slope back to the start. This would minimize the size of the drive unit you would need to build.
I had a funny situation two years ago. I had the full haunt set up complete with lightning and fog and one little boy was standing in the street disagreeing with his mother. He said they should not go to that house because it did not have a jack-0-latern out front. The rule was if the house did not have a jack-0-latern you were not supposed to trick or treat there. His mother assured him that in this case she thought it was alright. I added a jack-0-latern the next year just to be safe.
I had a fog chiller all ready to go last year but must have kinked the hose when I added the ice so it would not work. I simply took off the chiller and the Froggy's Freezin' Fog Juice settled just fine with no chiller at all. The conditions were approximately what you described.
Married with no children. Long time horror movie fan
Flying, chess and halloween
My love, sweet Queen and noble wife. I alone remain to bring delivery of your pain. Severed my darling, too quickly from this life. Of fires drawn and memories met, I shall hold our two hearts again in single time.