Yes it is supposed to be. Consult with an attorney for guidance.

Yes you should notify USCIS of the death.

Wait for USCIS to request medical.

Likely not but best to have an attorney review the case.

Consult with your attorney for guidance re: initial interview.

You should receive welcome notice shortly after I485 approval.

The I751 is likely joined with the N400 and both will be scheduled and adjudicated together.

You can file I360 with I485 pending and request case be held in abeyance. Consult with an attorney for guidance.

Best to consult with an attorney for full review of case.

$1225 is the AOS filing fee. Check USCIS webpage for guidance.