You did purchase the property in one tax year and are selling it in another tax year which satisfies one of the court rulings. 

Make sure your financial advisor understands real estate taxation, financial planning and tax planning. 

When we looked at what his cashflow is currently, and then considered what he would net out of a sale post tax, he decided to keep owning the properties.

@Shiloh Lundahl Awesome, thank you ok so having that 10-20k as a buy in is important, to first getting into it.... it helps get those first deals started.... just as an aside : I am also just starting out doing finder's fee methods - with tax foreclosure overages refunds, and assett recovery / state funds refunds... so I think those can help me to get that intial 10-20,000.... it might take me some months, but I think I can get there.... that's my initial plan, at leastAnd if I can get that saved up, then that will help me break into deals....

Have also used list source and prop stream before but the data they provide is very similar to what I pull off the tax records through CRS Tax. 

Finally, even as the landlords cash flow increases, depreciation should keep a major portion tax deferred. 

Be mindful of short-term capital gains tax, as profits from flips held for less than a year are taxed as ordinary income, and frequent flipping may result in self-employment taxes.While profits from flips do not qualify for 1031 exchanges (since flips are considered inventory, not investment properties), you can minimize your tax burden by deducting allowable expenses like renovation costs, loan interest, and holding expenses.If you're considering diversifying into rentals, explore opportunities to benefit from long-term tax advantages such as depreciation and lower long-term capital gains rates.

I have 2 options:- finance the construction pre-selling the apt, and take my profits (expected to be around 700K pre-tax); or- finance the construction with a 6-7%/year loan (collateral = my house), keep the 10 units, and once the building is completed in 24 months, rent them for circa 180K/ year gross.

I would recommend an STR for the best tax benefits and cash flow no doubt.

@Andrey ShostakA tax calculator would be nice.