But I don't know which one is the best to start, which things should I investigate and to what should I pay close attention.

@Adrian Tilley - I am starting to realize that 1400/m seems too high.The Number came from the very non scientific preliminary search using Zillow and Craigslist for comps.

(A recorded trustee's deed (or similar alternative) confirming the amount paid by the grantee to trustee may be substituted for a settlement statement if a settlement statement was not provided to the purchaser at time of sale.)The preliminary title search or report must confirm that there are no existing liens on the subject property.The sources of funds for the purchase transaction are documented (such as bank statements, personal loan documents, or a HELOC on another property).If the source of funds used to acquire the property was an unsecured loan or a loan secured by an asset other than the subject property (such as a HELOC secured by another property), the settlement statement for the refinance transaction must reflect that all cash-out proceeds be used to pay off or pay down, as applicable, the loan used to purchase the property.

The "units are occupied, please do not disturb tenants" is a curious sort of way to put things, it's true, but hey, it could mean nothing.You will need to investigate, and of course, part of that investigation will be to get into each of the apartments and look everywhere.

Your insurance agent who sold you the policy should be able to answer that question at least on a preliminary level.If you have an established relationship with a lawyer, definitely speak to him or her.

(b) To the fullest extentpermitted by law, the Manager (such person being referred to hereinas "Indemnitee"), shall be indemnified and held harmless bythe Limited Liability Company from and against any and all losses,claims, damages, settlements and other amounts arising from any andall claims (including attorneys' fees and expenses, as such fees andexpenses are incurred), demands, actions, suits or proceedings(civil, criminal, administrative or investigative), in which he maybe involved, as a party or otherwise, by reason of their managementof the affairs of the Limited Liability Company, whether or not hecontinues to be such at the time any such liability or expense ispaid or incurred; provided that no Indemnitee shall be entitled tothe foregoing indemnification if a court of competent jurisdictionshall have determined that such losses, claims, damages, liabilities,expenses or such other amounts resulted primarily from the grossnegligence or willful misconduct of such Indemnitee.

If the numbers match up with what you are seeing then it's looking good, if not there may be more to investigate. 

Looks good on paper, but the investigation will tell all.

I am currently in the planning process for a similar product so I can probably answer some questions if you are still investigating this process.  

It is possible to file a complaint with the Cook County attorney general......if they receive enough complaints they will investigate them.