To begin with, one doesn't throw parties for dogs. They're parties for dog owners/lovers who are throwing the party for themselves under the guise of it being for their canine buddies. Because, simply, dogs don't know from parties.
Everyday is a party (unless of course, there's abuse involved) and isn't it a shame that we humans can't/don't regard our "each day" like they do. Even so, a dog party is like a bark park with "cake". And, we humans are the ones hung up on an occasion like puppy showers or birthday parties.
Can be "free from disease" day, or "no fleas and ticks month" or "just got groomed". Shouldn't be that hard to be creative and find a reason for a party. "Had my shots", "Didn't pee in the house", etc. , are all, from a dog's perspective, big moments worth celebrating -- especially when we realize how much shorter their lives are than ours. Personally, I believe my dogs love celebrating TCIT -- Thank Canus (the great dog god) It's Today!
As far as entertaining everyone's dog -- don't think one has to. They'll either play with themselves or with the humans -- and, if there's food around -- a number of them will be strategically located.
Of course, it's best if the party is outdoors in a fenced in area. Make sure there's lots of drinking water. There can be games for those that wish to participate -- fetch, frisbee, pin the tail on the human, tug, etc. But again, most dogs can amuse themselves without our help. Just make sure all the canines are "sociable".
As far as etiquette...gonna be tough to have the dogs use silverware and napkins. Think the most important etiquette is that each dog owner needs to be mindful of their dog pooping and to pick it up immediately so that other dogs don't eat or roll in it which some dogs love doing!.
Personally, Curtis and Buzz and Coco love parties. But, like I wrote earlier, everyday is a party filled with wonderful surprises. Loved and cared for dogs never lose their wonderment and isn't that a joy of which we all should be envious.