1. Go to Docking Mode (View > interface > docking) and press Tab.
2. Not in this version. Guides are something people often need to add on the fly, without having to go into multiple menus.
3. We haven't removed any options for the Pencil; Smoothing only shows up if you tick 'Precise Mode'.
4. No, this would be really annoying to people trying to draw near the bottom of the screen, or use the tool/color pickers. You can switch apps quickly by pressing the Windows key, pressing Ctrl + H (you can change this in the keyboard shortcuts), or pressing Alt + Tab. Or change the taskbar so it doesn't autohide.
5. This is something we didn't get around to for ArtRage 5 (as we wanted to release before 2018

) but we'd like to look into in the future (it would require some backend changes to the layers, so we're not sure when or if it will happen yet, but it's on the list).