Hi PJ,
Yes it is possible to handhold this lens but when you are working down at the 5x end your dof is about 0.25mm. If you are going to hand hold it then expect it to be quite hit and miss with more OOF images as the magnification increases. I have found that its far easier to use with a focussing rail, I am not into bug images and most of my macro images are still lifes so I dont have to be worried about my subject getting bored and walking away.
You can shoot without the lights but only if you want to wind up the ISO or have long exposures. As your magification increases the amount of light you get falling on the chip/film decreases, three options, add more light, keep the shutter open longer or make the film/chip more sensative (ie bump up the iso). If you are intending to hand hold and not use any extra light then you will have to bump up the ISO and hope you dont get to much noise.
I haven't messed around with extention tubes however canon used to make (and they may still) a life size convertor for the 50mm macro, when you add the convertor it changes from a 1/2 life size to 1:1. The lifesize convertors can be hard to find as they can be used with the tilt + shift lenses to give you macro focussing ability with shifting and tilting.
Hope that helps
BearSummer