I hope this helps.The other thing to keep in mind is that, assuming you successfully convert the property to your primary residence, the capital gain treatment is different with respect to holding periods so you want to ensue you fully understand those rules prior to selling.

The issue right up front is that the property is your primary residence and so not eligible for 1031 treatment.  

Properties bought for rehab/flipping are held for sale and not held for rental or investment purposes and therefore to not qualify for 1031 Exchange treatment. 

Below is a small sample of the standardized costs I use.Window treatments: $60/window.

Property used primarily for personal use, like a primary residence or a second home or vacation home, does not qualify for like-kind exchange treatment."

In addition to savings like I mentioned above, a really good Realtor can often save clients in other ways, such as - making recommendations for the best and lowest priced closing attorneys, termite treatment companies, home inspectors, surveyors, etc.

Mom got brain cancer and I need to be close to her, a job relocation, my kid got injured and is now permanently in a wheelchair and the old house isn't wheelchair friendly, old house burned down, etc, are what we're looking for.The other alternative, depending on how much it'll cost you, etc, would be to refinance the duplex into investment property financing with a closing concurrent to the FHA purchase closing.

However, the seller is done a disservice because they aren't receiving the same treatment as the seller with the more expensive property. 

I thought I would be "kind" and let him stay until his treatment was over in 6 to 9 months.

Go with the EPA-suggested bleach treatment and you'll be fine.