A. Its possible to configure the taskbar to autohide (Start - Settings - Taskbar & Start menu - Auto hide - OK) but a number of people have asked if this can be set another way. Basically the answer is no :-(
MSDN says this:
"The taskbar supports two display options: Auto Hide and Always On Top. To set these options, the user must open the taskbar shortcut menu, click Properties, and select or clear the Auto Hide check box or the Always On Top check box. There is no way to set these options programmatically. To retrieve the state of these display options, use the ABM_GETSTATE message. If you would like to be notified when the state of these display options changes, process the ABN_STATECHANGE notification message in your window procedure.
The work area is the portion of the screen not obscured by the taskbar. To retrieve the size of the work area, call the SystemParametersInfo function with the SPI_GETWORKAREA value set. To retrieve the rectangle coordinates that describe the location of the taskbar, use the ABM_GETTASKBARPOS message."
So there is no registry entry way to change this.