We charge clients for a replenishment of hot tub chemicals - usually once per year, as well as $30 per month for pest control. 

Obviously more time and energy, but potentially lower risk and better project controls.

Is there rent control?

Sounds like you have a tenant, not a seller staying in the building.Is it under rent control? 

I’ve read a bit about looking for budgeting for Cap Ex, vacancy, pest control, property manager (in case I don’t end up living in one of the units) taxes, checking to make sure zoning is right.

I would like to build a Quadplex in Delaware in the very near future.

It would lower her rent and keep it controlled so she was in!

I detest the ESA law because it essentially wrests control of property management from the owners.

@Chasen Brown, You can for sure piece together a property management company but it is a lot of work quality control checking everything.

You can't control the future and it's good to dip your feet into a deal, learn about commercial real estate investments, and continue to optimize for future deals.