I found I was not able to get enough air when I was carrying a solid core door upstairs and into a bathroom (yes 100 year old interior doors are solid core) with a mask on.

I don't remember but if it didn't have a kitchen and bath on each level,  adding that and adding appropriate interior doorways could net you a 'real' up/down duplex or if easier to permit that way just a home with ADU.   

However, the inspector wasn’t aware of the interior leak, as it had been dry for quite some time prior to the inspection.

It has been quite a headache, but the property is at least at a point where I see no more major expenses (roof, interior, all in great shape).

The house was located in the country and needed new hvac, al new flooring(lvp main living area, carpet in bedrooms, tile bathrooms), paint, kitchen counter tops, new tub in master, new shower in hall bath, all new interior doors and knobs, all new light fixtures, newappliances, new 10x14 deck on back of house, fixed 2 windows and patio glass.

Basically brand new property except for foundation and exterior framing and majority of interior framing.

My latest property needs some light cosmetic work - new flooring (carpet and tile), interior paint, some interior doors to replace, and possibly new kitchen counter-tops.Additionally, have another property that needs to be turned after tenants vacate at the end of the month. 

Not full gut rehab, but updated kitchen (layout/paint), a wall removal, interior paint, vinyl floors  That kinda thing.Some PM's I have talked to have a construction side and inform me they can complete necessary contractor work so long as I hire them to manage the property.   

The best you can do is try to estimate interior needs based on exterior condition.

Updated interior and exterior.Appraised value: 245k on the second appraisal (the first appraisal was at 214k, since the appraiser was covering her tracks for a previous low appraisal on the same property some years back) This appraisal is still low, since there are no good comparable properties in the area.