Hi, Chrissy,

In 2017 and 2018, Portland Intown Contra Dance (PICD) partnered with Friends of Congress Square Park (FoCSP) in downtown Portland, Maine in putting on a series of outdoor contra dances.  Info about the 2018 series here: http://portlandintowncontradance.com/blog/2018/5/3/happy-dancers-dance-outside

Logistics: FoCSP is a nonprofit that has an agreement with the City of Portland, Maine to organize events in the park, but other organizations can do so as well through the Parks and Recreation Department by paying for an event permit and providing proof of insurance.  FoCSP provides the insurance for these events and fundraises money to pay performers for events throughout the season, including the contra dances.  PICD handles booking.  Both organizations do promotion.

Dancing on asphalt: It's not awesome.  I don't think there's anything else to say about it.  If people are dancing on concrete, you might tell the experienced dancers to minimize their stomping, if anything.  I do know someone who sustained an injury that way at an outdoor event in Cincinnati, Ohio.  I don't know if there's something you would need to say about grass.

Sound: At Congress Square Park, we shoot for 92 decibels.  We also make sure to comply with the municipal sound ordinance in regards to maximum decibels and how late an amplified event may run.

Dance repertoire: This can be so variable that a caller needs to be very very flexible in choosing and teaching dances.  If no more than a few experienced contra dancers show up, then you need to treat it as a community dance.  But even if a whole bunch of experienced dancers show up, the total number of dancers and the proportion of new dancers is likely to vary unpredictably throughout the event.  While the experienced dancers are more likely to stay for the whole event and dance each dance, the new dancers are more likely to drop in and out, which means that you cannot expect to build up the level of complexity in choreography over the course of an event, as you usually can at a regular indoor contra dance.  This variability is especially the case in a downtown setting like the events we host in Portland because people will stop as they're walking by, try one dance, and either stick around or more on.  

That's the info I got.  Good luck!