Determine what it would sell for on a comp-based approach as a 4 unit (they don't sell based on cap rates) and determine what it would sell for as a Cap rate 5 unit.

I would NOT recommend that approach at all .. its just as easy to lose your butt as to gain a little bit of equity do all that work..

This should simplify your approach and help you avoid legal issues for failure to perform under the contract.

Bonus depreciation can be a powerful tool if approached correctly, and has the potential to create substantial tax benefit, which can be used to offset the gains incurred from the sale of your rental properties.As you seek investments with bonus depreciation, keep in mind some property types will garner more benefit than others.

And then they lose that huge benefit of free tax writeoff vacations.Since you want to travel out of the country I'd maybe recommend a more passive approach like @Greg Scott said. 

I wouldn't think BP would want to promote  anything even approaching the question of morality. 

Any tips on how to document the damage effectively or how to approach the adjuster?

I personally use the income approach.

With your return on equity currently low and your desire to step back from hands-on investing, this approach makes sense.

Overall, it could lead to a more cautious approach to buying and selling, with more emphasis on long-term holds rather than frequent exchanges.