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're like someone who honks at a car for driving the speed limit and then looking away when they pull up to next you at a stoplight.  

It sounds like you have a good idea of what you are doing and are looking to speed things up for future purchases. 1.

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. 

What do you want out of a GC:  Someone who has lots of quality sub connections, someone who doesn't soak you with their fee on top of Sub costs, someone who will be there to oversee manage the quality and speed of your project at least 3x per week and be in constant communication through calls and pictures.