It would be much faster and practical to choose any given tool if they were all visible, all the time. There are 20 or so actual tools. I lean towards having all 20 in a single column, but 2x10 wouldn't be too bad either. Among other things, it would also make it more obvious which layer is currently live, if the toolbar button for the active layer were in a standout color.
Furthermore it would be very helpful if every tool had a tooltip showing its keyboard equivalent.