I have a photoshop file with many layers. I would like to put one layer on top where I can draw transparency, so that full white (or black) is rendered as 100% alpha, so it subtracts all the layers underneath. Is there a combination of blending modes, opacity settings, mask settings that can achieve this result?
What you'll need to do is place all of your layers into a single layer group.
From there you can add a layer mask to the actual layer group or you can place a clipping mask on the layer group.
To add the layer mask simply click Add Layer Mask at the bottom of the Layer panel.
The clipping mask is a layer that is placed above the layer group and is converted to a clipping mask by right-clicking it and selecting Create Clipping Mask (only available in CS6 and above for layer groups).