Is there a certain DTI ratio that you will usually consider acceptable for an applicant?

You'll get a feel for the age of the neighborhoods, the vitality of the commercial buildings, the ease of location, the closeness to jobs.The markets you're describing are more linear, and usually have lower capital appreciation.

It may sound nice to pay a 6% management fee but the extra fees can add up to be more than the other company that charges 10% with no additional fees.

It usually doesn't work that way. 

First, estimate what the renovation would cost, how long it would take, and how much extra you could potentially sell the property for once it’s fixed up.

In a soft insurance market, coverage is usually broader, lower deductibles are more accessible, underwriting is usually more flexible, and premiums are generally aggressive / lower. 

I ASSUME you’re talking $400+ in extra expenses for providing water, power, sewer, gas, internet, communal area cleaning, and exterior maintenance.

One thing that I would like to add to this list is making an investment without having enough extra money to get through the medium times as well as the bad times.

If you generate enough money annually to dismiss a W2, then consider covering the ever increasing costs of retirement & health care and those do not go at inflation metrics but usually way higher. 

Still, considering how difficult it is to find a good real estate focused accountant, limiting your search to local providers usually gives you too few options.Expand your search to include remote CPAs.