BP community. I realize there are many probate threads, so please direct me to them if these questions have already been answered.

I went to Lake County probate records in Park City, IL. It was easy enough to find out who the executor/administrator/petitioner of estate is and whether or not they have independent authority (e.g. full authority) over the estate sales. I ignored all records with Conservators, Guardianship, limited authority admins, or where the independent authority admin rights were granted to lawyers because the admins chosen filled renunciation forms. 

What I couldn't find and have questions about is this:

1. Letters of Office indicating the official judicial decree granting the executor/administrator the 'official' right to act in that capacity. Must the executor/admin provide this document before selling the real estate to me? If the sale is made prior to, does that void the contract?

2. Inventory List: When is this supposed to be added to the file to see what real estate the deceased owned? Will it show any liens/encumbrances? Can someone provide a sample of what the inventory list looks like?

3. Petition for Probate & Letters:  There is a document with same title that indicates personal estate value and real estate value, along with annual income from real estate. Some times the value is listed and sometimes it's 0, yet I know from the will that the owner had multiple homes that his survivors inherited, so how could the value be 0? Should the value be ignored?

4. Any other recommendations/suggestions on relevant documents I should look at?