Any Tips that are helpfull when scouting for a Location?

I am looking to throw some open airs this summer and need some tips.

What are some things that make a good/ safe location and what would be a dealbreaker?

How far should I be away from houses if i wanna run my subs at 140db (1m)?

Do 2x2meter Hornsub Walls already have a passive cardioid effect?