I have also heard conflicting directions on how to insulate the basement to deal with moisture which has been confusing.

Moisture is usually the biggest problem esp in high humidity. 

If so, the cavities behind it will hold moisture long enough to allow mold to form.

In addition to the owner-occupant requirement, FHA is fairly strict regarding condition of the home, like must have working oven, flooring issues, age of roof, no moisture problems on door frames, window sills, etc.  

It's not uncommon, if there is a poor seal around the pipe, for moisture or water to run down the pipe to lower levels of the house.

There are some sources of moisture to the crawlspace that were known and a couple more I didn't realize at first, but all can be taken care of I estimate:    crawlspace vents maybe always left closed,  condensate drains for furnace and tankless water heater not run to proper drains, just running onto crawl dirt, no gutters on house and grading could be improved on one end of house.  

Regarding property liens, you should be notified after title search is complete, do your inspections (termite, moisture, maybe even a home inspection and get a written report) My preference is single family homes vs apartments/condo/townhouse unless it's at a extremely great price and factor in HOA dues....hope this helps.

My first question to you would be, "Where did the moisture come from to encourage that much mold to grow?"

It is possible for roots to penetrate PVC pipe (SDR-35, etc.) at the gasketed joints, so regardless of what pipe ends up being used, be aware of the surroundings as well and be prepared for minimum maintenance.One final parting thought - consider an extra cleanout, maybe a 2-way cleanout just outside the house foundation, even if it is not required!

I do know a little about mold, in that you need some sort of source of moisture to get it started, which we figured out was coming from the crank-out windows in the bathroom, which even though they weren't that old, were wood windows that had warped enough to let small amounts of water in during heavy storms.