First, is it possible to add multiple rings that are not on the same plane?
You used to be able to hold down the control key to rotate a body independently of their rings, but I accidentally broke this when I setup using the Control key to select multiple bodies. I'll fix this in the next release (2.0.4).
So in version 2.0.4 you can create a ring, then hold down the Ctrl key as you rotate the body. Then create a new ring and they will be on different planes.
Secondly, how does one create a black hole?
I've just added a popup option to radius so this can be done entirely with the mouse (this will be in 2.0.4). And now when you choose to lock Mass or Density when you select black hole. Soon you'll be able to create black holes with the same density as the Earth.
Ctrl+W works (although this keyboard shortcut may change in a future release).
P.S. Did I mention this is the most addictive thing I've ever played?
Awesome. Thanks for your purchase.