Pay attention to the weather forecast that day - 2 minutes of ill-timed rain can really screw things up. And if you start sweeping in and it looks like the skies will open up, crack the whip like you're going to the glue factory w/ your horse if you lose.
When wetting down - use a very light mist - just enough to wet the sand and take the poly dust off the stones themselves - but this is a very, very light mist. Think of the hose nozzle/gun thingies that have 7 different settings you can rotate through, and the fine mist you get on the "Mist" setting. That's what you want.
As for base prep - do as you normally do.
This discussion has been included in the site beginner's polymeric sand page.