this will be a very common issue for the next few months.. its dial for dollars time.I would also be talking with the HML about extension and or lowering rate but keeping current. they cant foreclose so it would be in their best interest to work with you through this trough

Any other pitfalls (appraisals, etc) I should be aware of?

What is most important is that you know how to tap resources when issues occur, have common sense, and know the local ordinances. 

You can estimate vacancy by what is common in your area.

Its common for sellers agent in this market to pressure buyers by saying there is another cash buyer on the horizon.   

Rooftop decks/common areas are fairly common for the infill stuff I see.  

@Laura Blair How common is it for a municipality to allow for a shipping container home or tiny home?

I don't know any good search engines and my agent says it's not common to buy duplexes and triplexes.

If they don’t they will likely be no better or worst than a common lease tenant , but Unfortunately they may less concerned in paying monthly rent as they have both the law and the preparedness of knowing they were going to move , it’s like they have nothing to loose by not paying and than moving when they are ready.

Delayed closings and price reductions are very common over the last 2 weeks.