For your inquiry, best to consult with an attorney for guidance.

Yes you may do so with valid visa while case is pending.

No this should not detrimentally impact your case.

Option C is reasonable for interview purposes.

The online system is often not correct. Contact USCIS for guidance.

You should have indicated the children previously. Consult with an attorney for guidance.

It varies depending on the service center but likely 9-16 months.

Yes you should reapply since your marriage was less than 2 years at time of approval.

No it is not necessary to list all assets.

Contact NVC for technical support and guidance.