#4 is OK as long as the angles are equal. That would be an unusual situation for what we usually have to deal with, it usually doesn't come up.

I don't think "perfectly in line" is ever really achievable, particularly if there's suspension motion or any elasticity in the mounts, so what happens there is mostly an internet debate.

The actual u-joint angle does matter, should be equal within reason on both ends, but there is a vibration vs. speed relationship that Spicer has published (available on the internet somewhere). I don't recall the exact recommendation, but staying under 3-4 degrees should be ok for most of what we do. Again this shouldn't be a problem for most of us - where it comes in is with 4x4 trucks with lift modifications.