It might be more advantageous to pull the damaged dry wall and try to determine the source of the moisture penetration that is causing the mold.

It is often easier in a balloon framed house to bring the attic into the conditioned space than try to air seal the tops of all the walls.However, if you do spray and insulate the underside of your roof deck in most any climate, but particular in a colder climate, you will also want to insulate the topside of the roof proportionately to ensure the roof deck remains in a narrow temperature band and you do not have condensation/moisture collecting in the roof deck.   

Found out that the HVAC condensation tube was running to the outside gutter drain (previous owner did this) and unsure why this didn’t show on my inspection report... so, the pipe froze and backed up moisture causing the electric pilot to burnout.

Usually from moisture somewhere. 

But upon ripping it up, I found it to be soaking wet and layered with piles of dander/dirt, which due to the moisture was more of a mud -yuck.

"Looking at the possibility of using cinder block for small flex/industrial developments"Only know residential stuff built with cinder blocks, but get with a structural guy to understand:1) Is CMU (cinder block) cheaper for your design2) Moisture invasion - In apartments you build an outside wall of CMU and then cover it with frame/sheetrock, you'll get lots of condensation and, god forbid, mold.3) Structural integrity - I really don't know since I think earlier stacked CMU wasn't as strong as tilt-wall, but don't know.

Here in the Dallas area, our soils tend to expand and contract as moisture changes, so foundation problems are quite common.

If the bathroom ceiling it's a getting damaged from moisture, I will make sure they have a bath fan that  rated for the space and instruct them to use it. 

In that time I have collected enough rust (from all the moisture) to consider myself native.  

I think it is comparable to the Allure Ultra that is better for areas with potential moisture (bathrooms, basements, etc).