The biggest problem is if you get approved without interview and USCIS is not aware of divorce.
#3 is not the worst thing, yes you'd have to ask to convert I-751 and hope they give you enough days to respond to RFE.
Your case is pretty tricky. You need to separate ASAP (like, yesterday). You also need to give whatever your USC wants to make sure the divorce is finalized ASAP.
Essentially, you need to focus on divorce right now. Separate, get lawyer and prepare everything so when 6 months is up, you'll have divorce decree coming soon after.
Immigration is secondary, but important to keep in mind.