I tapped into the green/white wire with the blue wire clamp that came with the V1. When I did the hardwire for my E46, I didn't have any problems. However, I think the green/white wire is a little smaller. So, here's what I did to get a good connection:
I strip the green/white manually (and carefully) on a very small section where I was going to connect the blue clamp. Then, I built up the thickness of the wire by wrapping a few strands of copper fibers from another discarded wire, twisting the fibers around a bit. Once I connected the blue clamp, there was a bit more thickness for it to bite into. After I did this, the connection was solid. I had no further power fluctuations--sunroof opening, closing, whatever.
For grounding, I actually used a 10mm bolt to the right front of the overhead opening (as you're facing the front). I believe this or some other DIY called for a bolt somewhere up on the left. However, the only one I saw there was a too deep to get at comfortably. The one I used worked just fine.
One final thing: After I'd put everything together, I was a little concerned to see an SOS light/error on the dash. I thought for sure I had inadvertently disconnected some wire while fiddling with the connections for the V1. However, the light went away after a few start/stop cycle and I haven't had any further issues. :thumbup: