She's gotta be relaxed for work (even if she has to relax AT work) !

808 does get referred to with she/her in the game I believe, so technically yeah. It's like how CNMN is often referred to with he/him despite being a robot as well.
Could be a case of they have no gender but are just referred to with masculine and feminine pronouns

I feel she'd also have a Purugly (or a Glameow one of the two). Out of those options, Espathra would seem the best fit, though all options could fit !

She may have gotten her degree and qualifications, then perhaps focused on music later on in life (when she had good employability and security)
I feel Vandelay's standards would be incredibly high, so Mimosa must have the expertise rather than getting in through fame y'know