All of our self-storage run at basically 100% occupancy except for our most recent addition. 

Whether the seller was open to a buyer commission or not, I wouldn't put an additional cost into any personal purchase.  

FlashlightTape measure/Laser measurePaper/Pen/iPadBinocularsReceptacle testerLevelMarbleDroneRespirator/Face Mask/Eye Protection/GlovesAQI testerWater pressure gaugeThermal cameraEndoscope cameraKnife Good list, in addition in my truck; ohm meter, megger, magnehelic, steel ball, air compressor  generator, plus stuff I'm forgetting

In my experience in MO, land bank properties are very low priced (these are generally properties/parcels that weren't sold at the tax auction), but they often have significant tax liens on them that must be cleared in addition to the "sale price" AND they require a significant amount of rehab in order for the properties to be inhabitable. 

You and your legal, tax and financial advisors should review this transaction in greater detail, especially the PLRs, to ensure you understand the significant risks involved and are structuring the transaction as close as possible to the PLRs to mitigate some of the risks.

THEY ARE NOT LIMITED TO ONE PROPERTY.So, they can 1031 to 2 or more additional properties OR 1031 into a rental property plus a DST so that all the profits are used up in the exchange. 

I was fine with all these numbers.Then I met with contractors...First, I wanted to add a new bathroom and approximately 450 sq ft of additional living space.

If this isn't required, then most likely having the GC sign a completion guarantee to ensure the project gets finished and lender is not stuck with a partially complete asset is the case. 

My best advice is find a place that has a few rooms with square footage to add additional rooms and an ADU.

They can provide access to off-market deals and connect you with a network of contractors familiar with BRRRR projects. https://www.biggerpockets.com/business/finder/agentsProperty Manager - Choose a PM with Section 8 expertise to ensure smooth tenant placement and compliance with inspections and rent guidelines.