I really like her roller derby outfit too. A lot of people got upset that her outfits in this movie were too different and not comic accurate, but I think that having a wardrobe of unique outfits is perfect for a character like Harley Quinn.
Honestly I’d be ok with carrying outfits if they sticker with the red and black/blue color scheme. Kinda like how Alex Fierro in MC&TGoA has varying outfits all in the same pink and green color scheme. (Yes I know that most people won’t get that example and no I don’t care.)
I think if you want to make her a really unique character who actually deserves all the saturation in the DC universe that she's receiving, they should make her more like Lobo as far as her general roll in the DCU.
None. Gotham's had an amazing design after Ecco's initial suit in the final Season. That being where she went more insane and fought against fellow Gotham City Siren, Catwoman.