Bunny: Friendly, extroverted, maybe a lil ditzy but well intentioned
Cat: Smart, a bit edgy, curious, she's giving off "dissection is my passion" vibes
Panther (?): Pragmatic, laid back, probably the voice of reason, tired of the shenanigans
Fox: Easy-going, friendly, clever, quick-witted, don't wanna stereotype foxes but she looks sly, lol
And to answer your questions, the two main things I take into consideration are environment and personality. I want there to be a reason for why my characters dress the way they do (Is it a work uniform? Do their clothes and accessories serve a purpose? Why that hairstyle?). Apart from that, I just want their design to be appealing.
Appeal is hard to pinpoint because it's different for everyone. To me it's about how well things work together. The flow of the design and how well the colors work together are important, but I'm also shallow so I like pretty characters, lol.