my recommendation would always be to err on the side of over exposure rather than underexposure because it's much easier to take pixels away than it is to add pixels. I love the control that LR gives you when it comes to shadows and highlights, so fixing shots that are properly exposed or just slightly overexposed is not a problem. Any time you need to bump the exposure slider up past 1 full stop in LR, you're going to be venturing into that danger zone where the computer starts adding pixels and that's where you'll get that nasty grain in the shadows. I didn't look at your exposure, but if you were shooting at iso 100, it wouldn't hurt to bump it to 200 and go from there, it'll give you much more flexibility when it comes to aperture and shutter. I know a lot of photographers don't like to review every photo after they've just shot them, but when the subject is still like that and I have total control over the situation, I'll literally pause for 30 seconds after each snap and make sure that my exposure is proper and figure out what I need to adjust for the next one.