First, I have to say I agree with previous posters. Build it, and they will come. I also agree with the advertising, but I add this. Please
do tell your neighbors what you are doing. Warn them you're going to, most likely, increase TOTs in the neighborhood by leaps and bounds. Even if you only get 30 TOTs, that's 30 times what they usually get. Those who want to be prepared with plenty of candy will be pre-warned, those who want to avoid the deluge (and we must accept they do exist) can make plans to be elsewhere or keep the lights off that night. Either way, they'll appreciate a heads-up. Heck, they may even decorate themselves a bit now that there's a reason.
That said, I address the questions of single theme vs. multiple theme. There are ways to bind many themes into one, and I, personally, think that a cohesive story makes for a better haunt if you're doing a walk-through. Even if the binding is as simple as the following (a very short version of one theme we have done in the past.)
Two doctors built a rehabilitation facility for the criminally insane. Nobody knew how they turned violent,
bestial serial killers into placid, obedient automatons. One night, the FBI raided the facility and discovered the
horrible secret. The doctors had invented a machine that could pull out one's worst fears and turn them upon
the victim, tormenting them until they were trapped in their own minds forever. Rather than be taken to prison,
the doctors hit the self-destruct button, intending to blow up the facility, and themselves. Unfortunately, it
didn't go according to plan. The nightmares were set loose, driven into the land on which this haunt is built,
and now, they've begun to seep out again.
The rooms of the haunt were 'the nurse's office' the starting room where the tale was told, 'the nightmare machine room' where the ghosts of the doctors tortured their victims and attempted to get more, and then each room was based on a different fear. Snakes, spiders, burial alive, clowns, dolls/creepy kids, the dark, etc.. The rooms had nothing but that common thread to bind them.
That's my two cents.