From experience, if laundry included in the rent you will have people doing a full load for with just one T-shirt in the wash, leaving their laundry in the wash machine for hours and your water and electricity bill will most likely go through the roof (I learn't that the hard way). 

The age of the home is not as important as the age of the major components of the home, the roof, plumbing system, electrical system, age of paint and other building materials that may have lead or asbestos, variable expenses can creep up and kill an investment. 

Featuring updated electrical, new appliances, new interior/exterior paint, new millwork, & thoughtful finishes throughout.

Get good at looking at non cosmetic things like HVAC, roof, hot water tank and electrical panel and put those things in a separate list.

I need to know when was the plumbing, electrical, hvac etc last upgraded.

The tenants pay their own gas and electric but like most mf properties in the city, the landlord is responsible for water.

If you do not have individually metered apartment units (so you don’t know how much exactly each tenant uses), you can charge a flat number for the water / gas / electricity costs of running your apartment.

After electric, garbage, and everything else just the house rental is around $3200/mo (not including general expenses) all said and done.I want to buy a duplex somewhere and live in one side and rent the other.

The electrical, plumbing, and HVAC will probably need to be updated.

If you are not prepared to bring the unit up to a quality standard now, assume the tub surround issue is a likely indicator of leakage issues and possibly wood destroying insects as well, so start saving now for a big expense, and evaluate the overall plumbing and electrical systems (including replacing old outlets, switches, fixtures, and correcting any improper "handyman" work performed over the last 20 years by the prior cheapskate landlord) to plan for costly updates there.