a single family to a multifamily property is perfectly fine.Lastly to your question - You must purchase at least as much replacement investment real esate as you sold if you want to defer all tax.  

@Josh Roman I have one that’s two houses with three units on one tax parcel linked to a second tax parcel that has always been on one mortgage.

Same school district, property taxes etc.

About $900 a month after taxes/insurance/and misc repairs. 

Bare minimum for me is $20,000 after a flip (before IRS taxes). 

I think most of his flips are in inexpensive cities like Cleveland, Detroit area, etc. https://flipsystem.com/faq/I think $10,000 to $20,000 (before IRS taxes) is a really small profit margin.

Since Florida has no income taxes...

He is ONLY willing to sell by owner financing.I am not a tax expert in estate taxes, but my guess from knowing others who have had similar situations is that IF he sold it outright for say 300K, he might have 75K of taxes.

You should make sure that the rental revenue meets all of your costs, including the mortgage payment, property taxes, insurance, maintenance, and vacancy allowance, since monthly rental prices might range from $1,000 to $1,600.Property Appreciation: Take into account the market's expected and past rates of property appreciation.

For more precise estimates of rental revenue, think about speaking with nearby property managers or real estate brokers that focus on rental properties.Closing costs: Compute the closing expenses for the duplex purchase, taking into account attorney fees, title insurance, property taxes, appraisal fees, and loan origination fees.