I've moored my boat at Whiskeytown Lake for the past 8 years. There are new docks in place at both Brandy Creek, and at Oak Bottom. Your best bet is to launch at Oak Bottom where there are full facilities, including a store, gas dock, etc. You should call the Oak Bottom Marina ahead of your planned arrival to see if there is guest moorage available. This time of year, that should not be a problem.
The lake is great place to sail spring through fall. It is not very crowded, and there are many islands and bays to explore. In the summer, the temperatures will be very hot during the day, but evenings and mornings are wonderful.
Whiskeytown Lake stays full all summer long, and is not subject to fluctuating water levels, and does remind me of a mini-version of Lake Tahoe. The water is clear enough for scuba diving, and is warm enough for swimming.
The wind is highly variable on Whiskeytown, and there is not much of it in summer. The best seasons for wind are spring and fall. There is usually wind on summer days between 7:30 and 10:00 a.m., and then again in the early evening.
Don
The lake is kept about 10 feet below its summer level during the winter months. If you are launching in winter, I would advise you use the ramp at Whiskey Creek, as it was has sufficient depth at low water; however, make sure your mast has enough clearance to pass beneath the highway bridge that lies between the ramp and the main body of the lake. There should be about 32 feet of clearance during winter, but call the Park Headquarters to check on this.