Body Builder
You can open Body Builder in an empty scene and create an empty rig. If you do that, you see the standard process unfold and your Scene Editor will present you with a null named REPLACE-WITH-MESH as follows:
You can replace this null with the object you wish to rig. A good reason to start with a null is to see what the rig looks like without the distractions of geometry getting in the way.
Hiding Stuff
You can hide Markers, Bones and Planes with these toggles in any combination.
Parts and Symmetry
Edit Part-
Clear Part - Click on the red marker that indicates a root and click here. You will be asked to confirm
Marker Symmetry-
Keyboard Shortcuts
While the Body Builder window is active, up and down on the cursor keys mirrors the viewport up and down through items. If you are in fitting mode, which always takes place at frame 0, left and right will not change frame but sibling - left arm to right arm, for example.