I know DSCR lenders typically don't touch them.

Older homes will typically have systems that are out of date - even if only partially. 

However, required downpayments were typically 40-50%, and would be difficult without a residency visa.

Ensure you collect a proper security deposit (typically one month's rent in Florida) to cover potential damages.Your plan to increase rent next year makes sense given rising costs (taxes, insurance, and maintenance).

Typically, we conduct background checks on only the individuals who are responsible for the lease (primary resident) and/or cosigners.

The real estate investing industry uses "Classes" to rank property performance risk, but there's NO agreed upon industry model:(Here's what we use for our Metro Detroit market:Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

For example, if the typical rent per unit is $1,500 (3bd 2ba), my landlord at the time would have one unit with three rooms and four people within the unit (one person per room and one room with two people), each paying around $500.

That is very typical of the "advice" I see given by the students in his group.

The typical income from a free and clear rental would probably be $800-1500/month - and on a financed rental probably $300/month on a good day in today’s market.  

That's a typical scenario and could cost you $10,000 - $15,000 so that would be a good starting point for your reserve.But there's more!