i did one this summer. i had a good time doing it, having cycles of people tuned in and dancing for 8 hours in times square as part of a television show promotion. i worked with this dude out of memphis who's silent disco services are used in a lot of music festivals over the past year or so, including bonnaroo. any idea who you're teaming up with?
the only temporary issues i had were getting used to no monitor / house sound. i was given the option to switch between my headphones (used to cue) and using another set of headphones cued to the main out to monitor volumes. instead i relied on DJing in my headphones and switching between the cue / main thanks to that option on my mixer. the guy who provided the equipment for the silent disco assisted in monitoring jumps in volume.
another issue was DJing outdoors in the sun. i had to change the shading situation based on the direction of the sun. this also screwed with being able to see my laptop screen. visibility of wave forms was definitely an asset in this situation.
something that was fun in this situation that i normally hate doing is interacting with the crowd, using the mic. you can def shout people out on their dancing moves, tell people to "sing it" / "make some noise if they're having a good time", etc. and don't forget to flirt with the chicas.