fertilizerspike

What you're talking about is known as the "three-body problem", which is still "unsolved" in the context of gravity models. Orbital systems with more than two bodies can not be stable according to gravity models. No attempts are really being made to solve this glaring issue, but, of course, there is known physics that explains it that is consistently ignored.

"Hubble telescope is actually theoretically capable of seeing a very bright light source even farther out, for instance 30 billion LYs. Unfortunately there hasn't been enough time for that light to reach us; it will only have travelled half the necessary distance (ignoring, if you don't mind, universe expansion)." We have yet to find such a boundary as you suggest beyond which we simply can not see. We should expect to find one if "big bang" (an idea invented by a belgian priest) is correct.

The typical methods used to "discover" planets around distant stars are spurious. That being said, there's no reason all stars couldn't have planets around them, even "in habitable zones", and that these planets could have moons. Until such time as a reliable method for identifying them emerges, however, we can't conclude more than that.