If your are not charging for people to get in then you do not have to worry about codes ect. How ever you can still get closed down if things get out of hand (to many people, to much traffic , someone gets hurt, ect) Also take note as a home owner you can get sued if something bad happens (someone gets hurt, theres a fire) and your home owners insurance may not cover it, check it out. My insurance co. says they will cover it but I don't think they understand that there was over 1100 people going through here over two nights last year. The best thing to do is treat it like you are charging to get in and do every thing that you would have to do if that were true. As for sprinklers I think if you go to Lowes and get two nice size fire extinguishers you should be fine. There are people on this board that know a lot more then me so don't take what I am posting as the gospel. Good luck and happy haunting.