This is improper advice. The OP cannot enter the US prior to the sponsor. OP's spouse MUST travel to the US either before or along with the visa holder.
This is not accurate. Once an immigrant visa holder enters they US, he/she can IMMEDIATELY exit the US. The endorsed immigrant visa acts as a full-fledged Green Card until the plastic one arrives or one year after entry.
Have you already submitted a DS-260 for YOUR case? Yes or No???
This is inaccurate. Visa expiration is based on date of the medical exam...not visa issuance date. It could expire even sooner than 6 months after the medical exam.
****Moved to the appropriate forum area****
I would submit an updated I-864 and supporting documents. The consulate Officer has the option to require them.
I agree with @Dashinka and @OldUser. I would not file an I-751 if I was not legally required to do so. An ADIT stamp will supersede the date on the card. The plastic card as well as an ADIT stamp are just evidence of legal status. Legal status does not expire when the evidence expires.
Your case is a little different from the thread you replied to. Your post is perfectly clear. @Dashinka's advice is perfectly sound. All non-immigrants with a valid I-94 are free to travel freely within the US. Traveling 91 days after entry via a K-1 without having submitted a proper I-485 package would not be a good idea.
1. Wait until BOTH I-130s have been approved and sent to NVC, then
2. Submit fees and documents for both cases.
3. Once you have the DOS case number for BOTH cases, Contact NVC and the consulate and request they be interviewed together.