Naturally we push the limit to the point that the Housing Specialist might request a small adjustment to meet the calculations. 

Then, there is an adjustment for the tenant's income and finally an adjustment for the area Fair Market Rent.

You'll need to make adjustments as the utilities cost changes.

I know they adjusted voucher limits higher again this year and we'll be pushing for increases on ours when they come up for renewal. 

Lets shoot for $90k down, $150k gross per year, adjust for your COC calcs, once you throw in expenses, Debt/Interest.  

That doesn't necessarily translate in high real estate investment returns but you can make some money investing in real estate there (like it seems you do) and so it makes perfect sense that you do that since you live there.Those like me who don't live in Panama are likely purely looking at figures and comparing risk-adjusted returns with other countries where they can invest.

Use the public records for your offer, and negotiate hard, I would add in the special provisions that offer price is based on $x/sq.ft if the house is smaller than the listed sq.ft the price will be adjusted based on the sq.ft. 

Regarding running model / proforma - simplest to create something in excel that you can adjust the numbers on.

It just takes an extra step out of the bookkeeping when you automatically know what property it's associated with.

In addition, the section 121 exclusion does not apply to the gain allocable to the residential portion of the property to the extent of the depreciation adjustments attributable to the residential portion of the property for periods after May 6, 1997 ($3,000).