Here's some info I came across for #4 about the potentially dangerous situation a bad transmission poses due to lack of power. I italicized the relevant sentence for emphasis...
Slipping gears: Your transmission is supposed to stay in one gear
until you shift (with a manual transmission) or the computer does it
for you (with an automatic transmission).
If the transmission is
slipping in or out of gear without any effort on your part in a
manual, or sliding into neutral in an automatic, you need to get to a
mechanic immediately! This is a huge safety issue, because if you need
to hit the gas to avoid a dangerous situation, and you have no power
to your wheels, the results could be catastrophic. The problem is
likely worn or broken gear linkage, so if this happens, don’t waste
time – get it fixed. Of all the transmission problems we’ve talked
about, most of them won’t get you killed except for this one.
Gears Slipping This is unnerving at best and potentially dangerous at worst: when you mash the gas pedal to avoid an out-of-control
vehicle, the last thing you want is a transmission that doesn't get
power to the wheels. No need to scratch your head over whether this
is trouble or not: if it happens, you know it's time to have your