It could be soils related, poor construction, drainage, failed material etc.

(if not $50,000), fire hydrants ($20,000), Roads/sidewalks($600,000), setback review, brush clearing ($100,000), grading ($50,000), soil erosion abatement ($20,000), maintenance costs or neighborhood fee agreements/covenants, wetlands, water surface drainage, legal ($20,000), building/excavation permits ($30,000),  etc. 

Be careful of prairie soil, Montgomery has foundation problems in a few areas of town and it’s important to not buy in those areas.  

Quote from @Brad Sand: I think you have the right idea, with lowering your expenses first.

I've mainly been looking in North Atlanta, and the agent I am working with suggested areas such as Marietta, Dawsonville, Cumming, Sandy Springs, Woodstock, Doraville, and Brookhaven. 

When I first started, I found out the hard way about title clouds, IRS liens, buying land that didn't have legal access, water issues, soil issues, etc.

I plan to hold and operate the property for at least another 5 years.I'm leaning towards the regular dwelling route but one architect told me going the regular dwelling route might require Baseline Hillside Ordinance (BHO) compliance, hill/slope grading analysis, a soils report, hiring a fire consultant to design/engineer fire sprinklers for the SFR, and having a structural engineer design/engineer the entire house (SFR + basement).

you have some of the worst soils I have ever seen.. its called Yazoo Clay as in Yazoo city MS.. this clay expands and contracts like no other..

I was looking at Marietta or the Sandy Springs area, as I see both areas as having some good potential in the years to come.  

You say the "house plumbing works wonderfully"; with the drains full of roots and soil, it's only a matter of time until they start clogging and creating sewage backup in the units, so I would say you have no choice but to fix this now, and to fix it properly.