I agree with the lighting comments - spend your cash on the strobes (I use inon Z240s because they are small) and the triggers for them (Hedwig can help you out with triggerfish). One on camera and one off camera is a good start, two on and two off is even better. More than that takes a bit of practice to co-ordinate.
For the camera, go as wide angle as you can for caves. I use a dSLR and know nothing about m4/3 so can't help you out there. Good luck with your shopping!
- Mark K likes this