Welcome to TG Twinsen.

I'm not 100% sure I understand your question but if you want a shape appear on top of a selected shape, select it and hit Ctrl + K which makes a clone of that shape above the original. No need to keep adding layers. You can also use Shift + Ctrl + F or Shift + Ctrl + B to send it one step further in front or further back.

Yes it's quite simple to make a group within a group.