Just simple common sense. 

Common fees will include a set-up fee, a leasing fee for each turnover or a lease renewal fee, marking up maintenance, retaining late fees, and more.

Are these common now?

You asked about buying older properties and the biggest issues I have found is that roofs need to be replaced, HVAC needs servicing/replaced, and sometimes there are foundational issues (not super common). 

The market has definitely gotten more competitive, and it’s common to see BRRRR deals over $250K, especially given the high demand/appreciation in the area.

2-4 units are not that common, but builders are building them more now.

Commonly known as xxxx.

@Natali Cobb depends on what is common for the area.Also, you can put in your ad that W/D negotiable and see what the responses are.

It's common for traveling medical professionals to extend their contracts.

You will likely have common area lighting (interior and exterior), perhaps heating and cooling too.