You can start with the filing of the I130 to get the process going.

Yes as you are still within the period of authorized stay.

No you must provide documentation for the previous 3 years of income.

Contact NVC directly using their online system to inform them of the status change.

While possible to apply, it is unlikely.

Yes you can submit the I485 and await if I601 is required.

You can notify NVC of your intention to pursue the immigrant visa within the 1 year requirement.

The new petitioner must submit an application. You cannot simply transfer.

Yes you may withdraw prior to a decision being made.

2 years and 9 months since residence since on your GC.