Just because you replace the old working unit with a new unit doesn't guarantee that you won't have break downs in the middle of hot/cold weather.

If you give up today, you are guaranteed to never find a good deal.

I guarantee the fire marshal would back you up.You could be nice and offer to install a $200 bike rack outside the building, but I would not compromise on storing personal items in common space. 

While the rent is guaranteed, I learned that the maintenance issues far outweighed any rent guarantees.Section 8 conducts yearly inspections which is great. 

But, could I minimize risk of renter defaulting on payments for the 2nd property by turning this property into a section 8 housing unit with guaranteed income from the gov't?

While screening tenants properly is not a guarantee to avoid this, it certainly is the best way to do it.

But, could I minimize risk of renter defaulting on payments for the 2nd property by turning this property into a section 8 housing unit with guaranteed income from the gov't?

While you can’t guarantee this often you will get a gut feeling.

DSCR is about a non-recourse loan (secured by the property and the property performance, not by the personal guarantee).

The only quick number there might be is doubling the cost of materials to add in labor, but that's not guaranteed - some jobs have few materials and a lot of labor and others are opposite.