I would call a few termite companies to give estimate to treat.  

Don't rent to couples.Screen your tenants and treat it like a regular rental.

If I sell a rental that I acquired using 100% qualified retirement money from a Solo 401(k) and immediately deposit the proceeds back into the Solo 401(k) would I have to do a 1031 exchange purchase or purchases to avoid capital gains or is this treated differently within a Solo 401(k) retirement fund/plan? 

Your property can be treated as both an investment property and a personal residence.

In this scenario, where I’m going to have to hire a cleaning company and possibly treat the unit for the smell, I feel entitled to the security deposit.

I'm not used to dealing with roaches, but if you paid a company to treat it, there should be some sort of warranty for a period of time. 

I would likely treat the duplex as a long-term investment, focus on the cash flow, and disregard the fact that it's supposedly worth less than what I paid for it.

I mean to treat this purely as an investment property and will bite the bullet of living in a property for a year.

You have to treat everything with a business mindset.

. -- Lastly, does anyone have any insight on how lenders are currently treating individuals who have been out of work and have lower reported income due to covid?