We are divorcing following her affair with a coworker that started 6 weeks after commencing a new career and job.
Oof. Ouch I'm so sorry, lavarelic. Even when a marriage is struggling, discovering an affair is painful. I'm glad you have found happiness going forward.
3b: If negative, await a further 12 months and complete the divorce without consent (which the law here allows on 24 months separation). And carry on.
I wonder if the amicable stage of coparenting is happening because she holds out hope you won't divorce her? If you serve her, then she may dysregulate into less than amicable behavior, if divorce seems imminent (and there is no one else lined up to replace you).
How are the kids doing with the custody arrangement? How old are they?
How does your wife's BPD show up in her parenting behaviors?
If she is likely to dysregulate further, it could be that you want to document those behaviors and get some sunlight on them before the divorce is signed and sealed.