I would bring the current owner with me and have a face to face talk with the building officials and get it straight from the horses mounth with the current owner being aware. 

Assuming me and the potential seller reach an agreement on price over the phone or by email, what type of document or form would I need to make the agreed upon price official?

Over the last year and a half I’ve accumulated 45 units and haven’t done any official background check on any of the placed tenants.

I agree with @Matthew PaulOne of my rentals is a 3 story house with 4 baths, it's 2 blocks away from my "Official" job. 

See the official San Francisco Office of Short Term Rentals website here: https://shorttermrentals.sfgov.org/Best,Michael Young

Not in Texas, but you need to contact the zoning admin and verify what the property is officially listed as with the city.

I’m officially tracking your property to see how it ends up.

Usually they also require their official name to be the mortgagee on the insurance.Recently I received letters from a mortgage company for 3 of my properties where my purchase price was less than $100k each, but they want coverage for at least $160k. 

For purposes of this section, the following terms have the meanings given:(1) "court official" means a judge, referee, court administrator, prosecutor, probation officer, or victim's advocate, whether employed by or under contract with the court, who is authorized to act on behalf of the court;(2) "qualified third party" means a person, acting in an official capacity, who has had in-person contact with the tenant and is:(i) a licensed health care professional operating within the scope of the license;(ii) a domestic abuse advocate, as that term is defined in section 595.02, subdivision 1, paragraph (l); or(iii) a sexual assault counselor, as that term is defined in section 595.02, subdivision 1, paragraph (k);(3) "qualifying document" means:(i) a valid order for protection issued under chapter 518B;(ii) a no contact order currently in effect, issued under section 629.75 or chapter 609;(iii) a writing produced and signed by a court official, acting in an official capacity, documenting that the tenant or authorized occupant is a victim of domestic abuse, as that term is defined under section 518B.01, subdivision 2, criminal sexual conduct, under sections 609.342 to 609.3451, or stalking, as that term is defined under section 609.749, subdivision 1, and naming the perpetrator, if known;(iv) a writing produced and signed by a city, county, state, or tribal law enforcement official, acting in an official capacity, documenting that the tenant or authorized occupant is a victim of domestic abuse, as that term is defined under section 518B.01, subdivision 2, criminal sexual conduct, under sections 609.342 to 609.3451, or stalking, as that term is defined under section 609.749, subdivision 1, and naming the perpetrator, if known; or(v) a statement by a qualified third party, in the following form:STATEMENT BY QUALIFIED THIRD PARTYI, ....................

@Brook RiemanThere isn't an official standard.