Does a buyer typically provide the seller with an Estoppel certificate and ask them to have their tenants complete them, or is the seller responsible for providing their own Estoppel? 

The delinquent taxes are being paid by somebody whether it is the bank to protect their interest, heirs or a tax lien certificate investor.

ValuePenguin is a good source for the relative cost of insurance by state.Operational Costs - Costs like property taxes, insurance cost, state income taxes, regulatory costs (ex: time and cost to evict, rent caps, rent control, certificates of occupancy), inspections, rent control, etc., have a tremendous impact on your return.

The building I’m evaluating has a certificate of inspection from the state of NJ (green card) which says it has 4 units.

A few years ago, I did a ton of reading on the subject of portfolio theory in the process of picking up a CMFC certification.

I have personally done it after filing the Articles of Organization, but before my certificate of publication was complete.

As far as being a turn off for the buyer, I read somewhere that in the state of Colorado, if a property has been completely cleaned and got a certification that you don't have to disclose that it was ever a meth house.

That's easy, at the tax lien/tax deed auctions.What is a Tax Lien certificate?

Some are operating under the old 506(b) exemptions and are taking more of a self-certification screening approach.

Illinois requires a disclosure certificate, in other words a disclosure that is notarized.