For example, people who invested in Cancun when it was merely a coconut plantation have seen their money multiply by thousands.

The FHA Self-Sufficiency test, to your point, says take gross rent and multiply by *75% then back out taxes and insurance and it needs to cover the mortgage + PMI in order to qualify.

If you're just practicing, you can either use the quote from other nearby (comprarable) properties you've previously analyzed, or take the great advice of @Dan Maciejewski and apply a fixed multiplier to get a rough number that's close enough.It's mainly when you're running financials for actual deals, and therefore must get it right, that you'll need to engage an insurance broker's help.

I agree with your point about holding on to a multifamily with an ADU and not selling immediately since the property value appreciation will multiply over time.

So when I am estimate I take the length of the wall and divide it by 5 to get the total amount of beams I need, and then multiply it by $600 to get total cost. 

Overall, country of origin wasn’t as good of an indicator of quality as you might imagine; I’ve worked with good westerners sure, but also folks from say the Philippines that were just as good as someone from Pittsburgh.Effectively, I thought of them as a force multiplier; they’re ideal for work that isn’t hard and isn’t a good or cost-effective use of your time to handle yourself.

I like to look at the gross rent multiplier as well.  

You can multiply your efforts by outsourcing things best left to other professionals.I recommend the book Who Not How, by Dr.

Where he is a simple formula that almost nobody knows, but is very cool and I share it with my students:Here we go:Leveraged return = Cap Rate - interest rate (market rate expected to pay)multiply that by the ration of debt to equity (so if it is 75% it would be 3 to 1, or just 3)add that back to the cap rate and you have your leveraged returnExample-cap rate = 8%interest rate = 6%LTV Ratio = 75%8-6=2%2% X 3=6%8%+6%=14% annual leveraged returnSo now you have a leveraged number (back of the envelope), but who cares if you don't know what it means and how to apply it.

During that same time period you can multiply your net wealth by a factor of 10 with less risk in REI.