So I massaged the cabbage heavily with salt to get the brine water going, but then it got REALLY bubbly... it looked like I washed everything with soap! Is this OK? One side effect is that it made it really difficult to visually tell that the cabbage was below the liquid level... I tried to add a bit of water to help dissipate the bubbles but it didn't quite work, so now I'm just hoping I did a good job of pushing anything under.
There isn't anything wrong the the amount of bubbles you are getting; your brine looks fine.
Take this from A Beginner’s Guide to Sauerkraut (+ Fermented Vegetables), for example:
How quickly and how much it bubbles will depend a lot on room temperature. If your jar is narrow or filled to the top it can be helpful to place in a bowl as it might bubble over!
I tend to keep my sauerkraut on the kitchen counter, covered with a tea towel (to also exclude light) until the bubbling subsides, which takes 1 – 2 weeks.
So all you'll have to do is wait and the bubbles will go away naturally.