No management costs as it would be self managed, and estimated property taxes by the average of the past few years.

From a tax perspective, are there countries that are more friendly when it comes to tax advantages than others?

That's 50k a year gone and you are losing tax write-offs and equity potential.

Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

Did you have taxable income that could’ve been reduced utilizing tax strategies?

Not that I'm a proponent of borrowing just for a tax break, but the interest is a deductible expense. 

When it comes to being a real estate professional, it actually doesn’t have anything to do with your job title or profession.

@Rafael Ramos All your goals contradict each other:(1) Cashflow: buy Class C & D properties2) Appreciation: buy Class A & B properties3) Low Crime: buy Class A & B properties4) Why would you want your investments to lose money to lower your taxes?

I'm not familiar with tax implications of 401K (I'm in Canada). 

However, there is no specific holding period contained in the tax code or regulations and there is no "safe harbor."