Most anything you read about crock cooking usually tells you to place the veges on the bottom. Frankly, I like this approach because the veges do not dry out and it elevates the meat above the liquid thus not creating a braised product but rather roasted.
As for cook times I always heat any liquids first so they accelerate heat in the crock pot. Also start out for the first hour at high then reducing cook temp to low for the duration.
