, status of major building components (roof, HVAC, structural, electrical, plumbing), accounts receivable aging (are all tenants paying or is the $20,500 schedule rent?)

There is so much to learn between the ages of 18-22. 

Hi @Jinxiang XuFoundation repair is common but no pipeline replacement, it depends on the age of the property, but in your situation it could be due to the foundation work done.Service prices are in all ranges.

My question is: could the current tenant (age 59) remain in the property if she becomes eligible for Section 8 assistance?

The biggest factors, from what I can tell, are age and rebuild cost. 

Many of us on here wish we were thinking about real estate at that age.

Not to mention, the right system will enable your tenants to pay rent online, have a tenant portal, and all the other features that both tenants and owners need this day and age. 

Congratulations on building such an impressive portfolio at such a young age and achieving so many successes!

For (2), as properties age the rents you command decrease. 

They are starting to age out.5.