I don’t know what all the limitations are in Wavelab LE 9, but in the full version:
On Windows you can right click the Stop button in the transport panel to select that option. It’s probably Control-click on the Mac. You might try that.
Try turning on the looping button, then make a selection from Right to Left, then Play.
Other than that, there might be a preset for looping on the left of the Transport Panel.
In the full version of Wavelab you can split clips in the Montage to selectively apply effects non-destructively. In LE I don’t know if that’s available, but with Audio Files you can probably put effects in the Master Section and then in the Master Section Render dialog use Selected Audio Range - Render in Place to apply the plugs to only the selected area in the Audio File.
These things should be in the Wavelab LE 9 manual on the downloads page, although I haven’t really checked.