Or is this just a little spot of Mildew from unlived in house/moisture?

First tub stank because it was filthy and the water added moisture and it stank. 

-The back bedroom window in unit #2 has a broken seal and moisture staining between the panes - recommend having a window professional repair.

It is 100% your responsibility to report maintenance issues.Here is a list of items we want to know about immediately:Mold (within 48 hours)Drippy faucets, drippy pipes, or “running” toilets (within 48 hours)Moisture where there should be none (roof, under the sink, on a ceiling, etc.)Maintenance RequestsPlease submit your Maintenance Requests via email to: INSERT YOUR EMAIL HERE We are committed to responding to you with any questions and/or a plan (if necessary) within 48-hours.Your Repair ResponsibilityMold (from living conditions): Mold will grow if given the opportunity.

porcelain tile flooring, smoke and carbon monoxide detectors wired into the ceiling electrical system, the most sturdy screens, if built before 1976 you will have lead based paint issues, make things simple, plan to pay for trash pickup and provide containers with attached lids, can you provide outdoor clothes line (when people live on small budget they hand wash and hang dry which is hard on plumbing shower fixture and moisture)  where is it located?

The property inspection turned up roof issues - structural sagging, cracked joists, lack of moisture barrier, improper shingling. 

I'm looking to do a vapor barrier to reduce any potential moisture, Insects, raydon, just better over all air quality is what I'm going for.

Mold requires two things to grow: moisture and a food source.

I would worry about the moisture causing dry rot.

It's susceptible to moisture and water, so not a good candidate for finishing.At some point, a previous owner decided to put a shower stall and a toilet in the basement.