Howdy, welcome to the ECF.
In regards to your first question, I've heard virtually nothing but good things about the iStick 50W. I'm probably gonna pick myself up one for my RTA's and stuff.
Secondly, the only potential risk that we are aware of currently is from "burning" your e-liquid. This is only done by achieving extremely high temperatures. At this point, the juice becomes distinctly harsh, and you're likely also burning your wicking material. If your vape is very hot/harsh/doesn't taste right, it's likely you're burning your e-liquid, which we have some idea is not good for you. Beyond that, there isn't much evidence of health concerns around vaping. A lot of the concern lies in the devices, and not using batteries that are going to react explosively when pushed to their limits (also, just how about not pushing your batteries to their limits?) Additionally, there are some devices out there which I wouldn't recommend purely for safety reasons.
I'm of the mindset that vaping can't possibly be worse for me than smoking, and it's a choice between the two for me, so I'd rather vape. Maybe 10 years from now we'll find out something that we couldn't have expected, but I'm willing to take the risk because it means I'm avoiding a guaranteed early grave (if I continue smoking).
So in short, I'd recommend the iStick 50W. Maybe with something like a Nautilus Mini, or a SubTank/Atlantis if you're feeling adventurous.