My only real suggestion for what you have described in your setup is to let the finding of the scary stuff linger as long as possible!

My first Halloween parties were just free-for-alls...my guests knew all they had to do was dress up and show up. I always had a keg too...music, a dancing area, and tons of food. Scary props were never "introduced"...I just let the guests get freaked out when the time came (you know...when they have to open the closet door to hang a jacket, or use the washroom...hehehe) People always entertained themselves. Keep the food and drink coming and the music happening, and you will not have to do much!

The only problem with this type of arrangement is that you will never know who might show up at your door [xx(] If your guests are doing their own thing and hanging outside so they can smoke, they will attract attention! I started doing invite only parties with a theme and storyline the year following a bunch of "uninvitees" showing up with fireworks for my doorway!

If it's contained though...and you know everyone, I would just let them do their own thing....Halloween is a great time for people to loosen up...prentend they are something they aren't and just have fun!

Good luck!!!