I have thought about driving, heard it was very rare to go from sup to driver. I would have to be one from the outside hire, correct?
Yes, you would be considered an "outside hire". How rare it is depends on the building you work in. I've seen buildings that were growing in package volume (and adding drivers), that made it a plan to move experience sups to driver when the openings allowed. I've also worked in buildings that had very little package (and driver) growth. In those buildings it's difficult to get a driver job (as it is for the p/t hourly people who are waiting to move up to driver).
In either case, it's in your best interest to take a dispatch supervisors job. If you are good at supervising people on the local sort, and you become skilled in dispatching, you improve your chances to move into a full time position when one is available....good luck!