Also think about what can be damaged (tenants generally don't take care of the place as well as you would). 

Poor communicators, poor housekeeping skills, prescription med abuse, big dogs that they couldn't properly care for, damaging, etc.

Every flip is like peeling back layers of an onion, but this one came with tears, sweat, and the occasional scream into the void.

This is one of the things that @Matthew Irish-Jones mentioned above - be careful about putting #3 on his list above #1 and #2.

If the structure on the property is determined to have no value, be careful when you consider paying the “value of the land”.The value of raw land is different than the value of land with an existing structure, even if the structure has no value.  

I have learned once again, No one cares about your properties like you do.

Renting to section 8 you really have to be careful.

Staff often seemed to focus on one requirement at a time, and only moving on to others as each was taken care of, instead of starting them all at the same time.

I don't care for this.

I don’t know how common vacancies are but I would say I could cover about 4-6 month in case of an emergency