BetterSense, when burning in a sky using split grade you need to think about the overall feel you want for your sky. Let's say you figured out your two base exposures and you just made your first workprint. Now you like the sky you have, you would just like it darker. What you would do then is keep the ratio of g00 to g5 when burning. So if your base exp. is 10sec g00 then 10sec g5, you would burn equally after each exposure with each filter for the same amount of time. If your base exp. is 10sec g00 then 5sec g5, you would burn twice as long after the g00 as you will for the g5. Another example; Now lets say you like the highlights in the clouds of your sky, but the blue part of the sky needs to be darker to create more separation then you would burn exclusively with the g5 filter. You have to be careful when you do this though because it will start to become grainy and look harsh quickly when burning with such a strong filter. More than not you're going to need to also burn a little with the g00. If you're worried about losing tonality in the highlights of the clouds, you may need to dodge them a little bit during the base exposure (g00), then when you burn the sky in as a whole that tone is brought back into the clouds, but also the rest of the sky as well.
As far as the portraits with the harsh lighting, try dodging during the g00 exposure on the dark side of the face. This will bring the midtones and highlights up on that side of the face. As for the brighter side of the face I would just burn slightly with each filter.
Hope this helps.