Grats on day four! As far as too much? I'm not an expert, but I would assume your body will let you know. At least that's what i go by. For one, I try to limit myself like I would an analog, even though it's so easy to just keep vaping away. I feel ya on the wanting an analog though, it was about on my day four or five that I thought I was gonna lose it and grab a pack from the gas station. But, I just soldiered through it and had my e-cig handy at all times, and now I'm closing in on the end of week 2 and analog free. I'm a creature of routine, so that basically how I vape, just like I used to smoke. I don't know, but that helped me for some reason. Once you hit the week two mark, the cravings for an analog seem to diminish, and as others have stated, all you'll crave is a vape. I plan on getting some 0 percent juice just so I can pacify vape more often because that was one of the reasons I liked to smoke, the actual smoking part of it. Overall though, I think you would have to vape ALOT of very strong juice to do any damage. The only other thing I can think of that could be harmful would just be the unsafe handling of strong uncut juice, and it being absorbed through the skin. In that scenario you'd just use common sense when handling the juice I suppose.
Anyways, once again grats on day four, and it'll get easier and easier.
Happy Vaping!