Hard to say. If you have lost two gears, there are serious transmission problems and it is only going to get worse. I've driven my car for about a year at 55mph, 30 miles a day, 5 days a week and once in a while for store trips.
Overdrive is the normally allowed position
until you face a wall.
Overdrive is a gear that was made to help conserve gas. It is best to use this gear when you are driving for long periods of time at a steady speed.
Yes, you can drive without the Supercharger belt for as long as necessary.
It will wait as long as you have it in "park." Put the baby in Drive or Reverse and off she goes!
Overdrive allowed is the NORMAL position ( if I'm on the highway and have to go down a long / steep hill , I like to cancel the overdrive with the switch on the end of the gear selector so the transmission stays in drive and gives some engine braking )
Zero days!
Indefinitely.
As long as this is an automatic car (manuals are very very rare) put it in D for drive and ignore it. If it has an OD for overdrive that is good as well.
5 without traffic.
The transmission is messed up, try playing between neutral/reverse and drive, my old Hyundai excel did that and the transmission did a weird sound then went back OK, but not for long. Recommended to change it.
Impossible to tell without knowing how long it took to drive.