What is the safest distance to drive by yourself? Me and my wife are relocating back to St.Louis from Fort Lauderdale next week. What is the safest amount of driving to do by ourselves we will be following eachother? Also where do you think the best stopping point would be?

 What is the safest amount of time to drive by yourself.?
Depends are you packing up the car for three hours before you start? Are leaving first thing in the morning after a nights sleep or after a day at work. ONLY YOU know when you are tired . Only your wife knows when she is tired.
It is about 19 DRIVING hours.
Did you plan on stopping for gas, something to eat or maybe a bathroom stop?

For planing purposes budget your time for two nights of sleep. You could do it in two days if you want to arrive at your destination exhausted and vulnerable to accident a few miles from destination.
With stops for food and gas your driving time is closer to 22 hours.
Have you taken into account things like rush hour traffic or construction delays along the way? In traffic expect it to take about 24 hours.on the road. Two long days of driving and a short one to finish.

Drive as far as you can the first day and then adjust your schedule as circumstance dictate for second day and the third day of a few hours driving to arrive awake and alert for the next part of your adventure.

Some can drive 12-14 hours a day others can drive 6. Only you know how many you can HONESTLY drive. 

When we go anywhere we take the same car, but seeing as you will be in different cars, drive until you are tired. It is extremely dangerous to drive tired, so I would say drive from morning to night, when night rolls around, either pull over or find a place to stop for the night to sleep, wake up early, and repeat.