Here are flash tables for using the built in flash with manual lenses:
Using the middle set of figures it looks like you should be using f/5.6 at 10 feet (around 3 meters) and ISO 200 with the shutter speed set to 1/180 or slower depending on ambient light levels.
Macro work is possible with flash diffusion or ND filters, assuming the lens doesn't block light travelling from the flash to the subject. Even with a lens in the way it is possible to bounce the flash off of a diffuser and towards the subject.