@Michael Lutes,The short answer is this:[1] In the RM-1 district, the minimum lot area required per dwelling unit is as follows, provided that, whenever the calculation of permitted number of dwelling units results in a fraction of a dwelling unit, then the number of permitted dwelling units shall be rounded down to the nearest whole number: 325(.a) A minimum 360 sq. ft. of lot area is required per dwelling unit for the first 1,440 sq. ft. of lot area.(.b) A minimum of 480 sq. ft. of lot area is required per dwelling unit for the lot area in excess of 1,440 sq. ft.; provided that, if the green roof conditions set forth at § 14-602(7) are met, the number of units allowed is 25% greater than indicated by the foregoing lot size requirements, applied prior to the inclusion of any other applicable increases in allowable units.Click the link below for zoning use chart: (Table 14-602-1.A)https://codelibrary.amlegal.com/codes/philadelphia/latest/philadelphia_pa/0-0-0-154712#rid-0-0-0-170236You also have to check if you are located in an overlay district.

Not necessarily a SFH so when one unit is vacant u still have another to pay for mortgage vs a SFH when empty (though low turnover) the payment comes from your cash reserves.

During due diligence you will inspect each unit.  I

That doesn't mean your strategy doesn't evolve, just don't run after every shiny thing you see.I would recommend that you find the area you want to focus on and then use your capital to house hack a MFR property. 3- or 4-unit is preferable.

In reality, they are at the garden level and the two floors above.The garden unit is only about 2 feet below grade and is otherwise a regular unit... full size windows in every room, high ceiling, front and back door, separate utilities and ventilation.

An empty unit is far easier to manage than one filled with a late or non paying tenant.

In a larger unit I think it is also uncommon but some places do use the demand billing to apportion costs if it is legal where you are.

Thus if I say a 10 x 20 “Foot, not meter” unit is $120, then yours would be around $40.

Though $200+ per unit is not super common, it's also not unheard of... especially with lower income tenants.

I'm not from your market but my team and I occasionally achieve the super host status whenever we launch an STR!