Hi, in August you can stay on the north shore or south shore whitout worrying about rainy periods like in fall, as windsurfers it doesn't mater but for wife and kids it does! In the summer, the long period swell will be on the south shore so if you are planning to surf or expose your familly to surfing, south shore got better setup so I recommand Kihei, the begining of kihei...and you can also windsurf there on good swell, place like sunset or one of the Kamaole parc could be epic.
If you've got kid, you need a pool to chill out at the end of the day with all that sun and salt and sands and wind. Again, in Kihei you can rent decend condo at luana kai and maui sunset and others. It's a small ride to the north shore...and not too far to Lahaina and other spot you might want to visit and surf.
If it's 100% boardhead, windsurfing root and culture, check for a house in Haiku and start your day with a coffee at the canery and chat with the goya and quatro crew every moring!

For gear. If it's more than 2 weeks bring your gear, i had a fabulous service flying with air new zealand when I visited Australia and my flight was from Maui to Cairns...so probably doable from major city!
Cheers mate!
BTW when I Go for shorter period, i rent from Matt Pritchard. Hi-tech as mentionned is very well furnished and well place to swap gear.
Usually in summer, 3.7 to 5.2(rarely 5.2) and 80l and less, unless you weight 100kg