Walking 500 miles would take quite a long time and you would certainly need to take a lot of breaks to make the 500 mile walk.
If you walked at a moderate pace then you would or should cover at least 25 miles per day during your 500 mile walk.
So if you walked 25 miles per day everyday then you would cover 500 miles of walking in 20 days.
But that is if you just kept walking everyday without stopping for breaks for a day or so.
If you stopped and rested for a few days in between walks then it would take you around 30 days to 40 days to complete the 500 mile walk.
You would certainly get a lot of exercise and should lose a lot of weight during the 500 mile walk.