since nobody has addressed my question about being exposed to winter rains here in Seattle, does that mean this won't be a problem (it won't be too wet)?
Literally, Auk gave you your answer in the first comment:
Too much water is not great - but so far all my junipers handle it well. Of course they are in well draining soil.
In other words, yes they can handle a lot of rain if the soil is well draining.
To address your light "issue": in winter, trees are dormant. That means that they'll slow down their photosynthesis and stop growth (it is a little more complex, but I don't want to get too detailed, because I might do it wrong too). This happens because of the lower temperatures and because there is less light. Because there is less light, the plant slows down their photosynthesis, because otherwise he would use more energy than he could produce. With trees that keep their foliage, there will still be a bit photosynthesis so it needs a bit more light than a deciduous tree, that you can store in pitch blackness because they have no leaves (which happens because the tree takes all the nutrients out of the leaves to store in its trunk as a kind of "fat reserve" for winter). To make a long story short, your juniper doesn't really need a lot of light in winter, but is still needs a bit (in my opinion, just give it your best spot)