Complex sentence: Construction started in March 2014, and is expected to open before the 2016--17 NHL season, the arena will have a seating capacity of 18,641 as a hockey venue, and 20,734 as a concert venue.
Split into simpler sentences: Construction started in March 2014, and the building is expected to open before the 2016--17 NHL season. The arena will have a seating capacity of 18,641 as a hockey venue and 20,734 as a concert venue.