This now has a masterfully crafted poll to go with it. I anyone would like to add options, please inform me.
I've voted :-)
already have a bunch of things on my calendar for summer, so I'm avoiding ticking the general availability windows. I may even be somewhere in the netherlands for a gig we've been asked to play on the second weekend in July, though I think that still depends on how much they're willing to pay towards our travel. In general, most weeks in the late July/early August window are fine for now, though that's peak season and everything will be super-expensive/might already be booked up.
Finding affordable accommodation for everyone might help narrow down the location. Getting a rough budget, and checking other constraints (who they'll share with, food/health/accessibility requirements) might also be a good line of attack.