There is no definitive answer to this question. Different players may have different methods for achieving flying cars in the game.
No, the regalia cannot fly.
Yes, there are multiple endings in FFXV. Some people believe that the game has more than one ending because there are different endings for different characters and items.
The regalia is slow because it has to be made from many different materials and it needs to be made in a specific order.
Some regalia Type F items are made from leather, cloth, or other materials.
There is no set speed for regalia. Depending on the source, it can take anywhere from a few hours to several days to travel from one place to another.
Yes, choices do matter in FFXV. In particular, your choice of class and weapon can have a significant impact on your playstyle.