The open water isn't necessary, just make sure you keep your substrate wet enough, much easier!

As for the water bottles, I do that. It helps stabilize your temps since the incubator doesn't have anything to hold in the heat when you open the door. When you put the water bottles in the incubator and open the door you only lose a few degrees, unlike when you open the door without them, I was losing as much as 10 degrees by the time I got the door shut. That can obviously cause spikes since your thermostat is trying to make up for the difference quickly. The water bottles are also really nice because if the power goes out they will hold the temp for a few hours.