Few things to note -
Batman doesn't exist, so in turn the Joker doesn't exist.
Wayne Manor has been in disrepair for many years, also there is no batcave under it besides an actual cave of bats.
You can become canon villains and heroes of Gotham with the exception of the Batfamily. Villains will be judge on a case by case basis, if their origins involve batman they will need to be changed in order to fit the history.
Wayne Enterprises have been on the decline since Thomas Wayne's death allowing other companies to move into Gotham.
Arkham Asylum still exists.
OrganizationsThe Falcone Family
The Maroni Family
GCPD
The Night Watchmen
Ace of Spades
IC: viewtopic.php?f=31&t=410116