When we went to Leipzig for the friendly a few seasons ago - stayed in Berlin and then took the train to Leipzig
For travel to the ground from the town centre, there is a tram to the ground, although it is a fair walk to the away end, and then lots of steps up to the turnstiles to enter the ground, you need to be fairly fit to climb them - hopefully they have improved the stadium as it was just a concrete bowl, and needed a few quid spending on it to bring it up to date.
The only issue was trying to get back to Berlin after the game, as they cancelled the trains so had to wait a few hours to get a train back, so you will need to check the train timetable to ensure that you can get back to Berlin - if not could be worth booking a nights stay in Leipzig.