A good starting point would be flash on ETTL, camera full Manual, ISO 200-400, aperture f/9-11, shutter speed 1/200 or so.
Think of it as just a fill flash situation. Try getting the exposure 1 (maybe 2 depending on situation) stops under, and let the flash do the rest. Might need to play with FEC a little if the flash is coming out too strong.
You need the apertures around that mark for 1:1 shooting to maximise your depth of field. Much higher than that and you'll get diffraction softening and images won't be as sharp.
As you shoot higher mags you'll need to open the aperture even more to f/9, f/5.6 even. DoF will be razor thin, that's why the top guys start using focus stacking for sharp images with greater depth of field.
Hope that all makes sense.