I have consulted the Oracles, inspected the chicken entrails, read the tea-leaves, and thrown the dice, all to determine that Saturday the 17th of July will be the most appropriate night for the case swap.
Long term weather forecast is for a brisk but cloudless night, with little chance of rain, and a good chance of drunkeness*
Can't help with hosting, as our rear postcard/backyard is large enough to hold either the beer, or the drinkers, not both at the same time.
* - Any complaints regarding actual weather conditions should be taken up with aforementioned Oracle.