I will definitely screen my buyers more in depth in the future to prevent this from reoccuring. regarding the continued marketing clause, I came up with this to include in my contract. 

Whether it’s learning how to build a property portfolio, understanding financing options, or managing tenants effectively, having a structured approach will keep you focused.This clarity prevents you from wandering aimlessly or jumping from one strategy to another, ensuring that you stay on course toward your investing goals.5.

My question would be, is this a good idea, or am I creating unnecessary complexity in the business structure? 

Or are there ways to prevent this?

The 5% down option was a great counter to the self-sustainability test that prevented a lot of people from taking part in the American dream and buying multifamily property. 

There's nothing preventing you from looking at replacements properties prior to closing on the property you're selling, You can even be under contract before you even close on your relinquished property.

Evictions, resident's passing away, posting notices, doing preventative maintenance walk throughs, resident complaints, neighbor complaints, skips, move outs, turnovers, emergency maintenance, etc.I used to be strictly on the ownership side, from 2016-2020 I hired property managers.

@Basit Siddiqi true. the other side of the coin is with rehab situations sometimes there are issues with the property that prevent lenders from getting involved.

The 4th Thursday of every month is a standing inspection for fire prevention to check all smoke detectors and CO detectors.

Finally, make sure that your short-term rental (STR) meets IRS requirements and doesn't get classified as long-term or this could prevent you from leveraging this tax strategy event though you are materially participating in property and it was placed in service.