So we held the memorial for B's sister on Saturday, in a pleasant and utilitarian Sunnyvale park building. All the picnicing and so on was on the other side of an artificial lake, so we didn't interfere with each other.
As the person who rented the room and hence was responsible for ensuring we used it correctly, I found everything was easy. The city worker who opened up the room was helpful to deal with, and when he came back at closing time we'd already finished cleaning up (we were allotted an extra hour for that) and he pronounced our work OK, so we'll get the deposit back.
The attendees were mostly either family or Jo's co-workers in emergency services co-ordination. After a little nudging, they were moved to tell reminiscence stories, ranging from Jo the auntie to Jo the Hawaii vacationer to Jo the master emergency services coordinator. And we all wore Hawaiian shirts and ate from the catered Hawaiian food that was spread out on the front tables.
Nobody tried to smoke or drink alcohol (prohibited activities). Nobody got too rowdy or loud. There weren't many spills and those easily cleaned up. The blue painters' tape held things in place but was easily removable. At the end, everyone who was still there pitched in to wipe down the tables, sweep the floor, dump the leftover ice, pack the food up and take it away, etc.
All taken care of. I hope that Mythcon goes this well.