Good Question Brenda! Glad you asked -
...costumes? Oh hell, bring 'em all! :-)

Weather?
Right now it's about 75, clear and sunny, and quite windy, probably a steady 5 -10mph with gusts of 20, for about the past hour. The forcast is for temps between 76 daytime high and 47 low at night. It is very (very) unlikely that it will rain. I would count on it being windy about 25 % of the time. Right now, if I'm out of the wind, it's quite warm - makes you want to lay out and get a tan. In the wind is another factor depending on what yer doing, but it feels quite cooler. Same at night. There is a forecast of some cloudiness this weekend, if so, the upside is the nights will be warmer!
There are good places here to get out of the wind, and to keep warm at night - we'll have a big campfire (when the wind permits), burn barrel, and of course the Ruben's Tubes heated spacious and accomodacious indoor audio-visual expressive toy experience FreekyTiki Lounge! And some parts of the house will be open too. Oh, and theres the hot tub :-) [take a number?]

Shoes?
I just wanted to add a thought about shoes - most of the grounds here are very hard on bare feet. 'K?