So it is entirely possible that you could be required  to accept somebody with ZERO verifiable cash income,  for example being required to accept somebody who mathematically won't be able to pay all the rent  (say they have $1900 sec 8 voucher on $2000 rent with 3x income ratio,  and $300/mo SNAP benefit, and zero verifiable cash income)  If you get that situation,  contact an attorney before doing anything else)FWIW if you have reasonably strict criteria on prior landlord reference,  credit,  etc. 

There are plenty of metrics I've seen people use that determine the most prudent time to sell mathematically based on cap rate, COC, ROI, IRR, etc. but the big x-factor in these calculations is future performance based on both appreciation and rent increases, which haven't been following a predictable linear pattern lately at all.

They're directly/mathematically related - reciprocals.   

That's is a simple mathematical setup that tells one without doubt, a SIGNIFICANT INCREASE in unit costs is coming. 

@Danny McGreevyPutting down a smaller amount and investing providing you have some hold time is mathematically better.

I have proven this mathematically in previous posts.A good lesson for you all to learn is to fact check everything you see using logic and common sense.Good luck my man.

From a strictly mathematical standpoint, you have debt on the house at 4.8%.

If we rope the expense in with rent and assuming 20% down you’ll see appreciation gain of 20% year one reducing to 4% at year 30.You should build a better mathematical model before your purchase but at slightly negative on cash flow, I am expecting returns of 13% over the first 8 years with an 8.5% interest rate on the mortgage.

For those who might be mathematically challenged, let's break this down...You just said that a professional tenant could live in your unit for 18-36 months before you can evict them and it could cost "easily...10 times" the $15K price of training. 

But they were just mathematical speculations on the success of mortgage bonds as a whole.