If you can’t quantify risk and don’t understand the mechanics of “weighted” average of expected return and range of returns (standard deviation) then you are at a severe disadvantage and should consider a competent investment / financial manager for your investment capital.  

If it is block construction the engineers will make you beef up the slab and add piles to support the new weight of the second floor.

There is a lot of weight on marketing, and a lot of inputs to that cycle.

After weighting all of that, does it make the most sense to try to keep this tenant in place? 

yep your weight in gold.  

They may or may not have good reasons and unless they communicate those reasons and perhaps even substantiate them I really try not to give them any weight.

I find with ANY project on a property, PLANS are worth their weight in gold bc they will show the exact inches, ft, etc that the project entails.

Check bed frames and chairs for their weight limits. 

BUT for certain rural areas it's worth it's weight in gold because of the reliability factor vs an unreliable or expensive existing utility structure. 

If it turns out well a good lender is worth their weight in gold.