That money is become too easy to secure so asset prices will get over heated. 

Houston looks nice compared to Miami !

If you intend to hold onto the property, or are just inclined to do your rehabs correctly, get a unit that is properly sized for your ducting and sq footage.FHA HVAC equipment that is oversized for the installed ducting is prone to shorter life span due to short cycling and potential cracks in the heat exchanger since the ducting will not allow the proper amount of air to be moved across the exchanger.

I know summer is getting heated up and almost ready for schools. 

A typical complete system for me typically runs less than $5000 (gas furnace and AC) Using existing ducts.A heat pump (which you probably wouldn't use there) is about the same.

Would anybody with experience on retrofitting an older duplex with central heat and air feel like offering some advice on how extensive that project can be?

Until the back taxes are paid t people had this mobile home before didn't pay it now we have to pay it we need the electricity turn on as soon as possible because we take medicine that we can't be in the heat we are going to end up in the hospital with a heat stroke if we don't get help so please help us to get the electricity hooked up please 

Do you have natural gas piping to your property because that is the least expensive way to heat with the exception of solar or some sort of rare underground thermal heating.

(Please consider the fact to get a mortgage with 3.5 - 5 % down payment I'll need job verification w2 which I had till March for 2 years but I changed my career in March and started as a self employed)Miami, Florida I'm not sure If different lenders in the market matching my situation?

That being said I actually ran your numbers through a proforma I use and here is the break down for that: Purchase price: 129,900Effective Gross Income: 22,086 (vacancy 10% of gross income; 2454)Expenses:Expenses%EGITaxes $ 4,618.00 20.9%Insurance $ 1,500.00 Heat $ - Electricity $ - Water / Sewer $ 1,200.00 Trash / Recycling $ 180.00 Lawn / Snow $ - Management $ 2,208.60 10%Repairs $ 1,104.30 5%Capital Expenditures $ 1,104.30 5%Supplies $ - Accounting / Legal $ - Miscellaneous $ - Total Expenses $ 11,915.20 54%NOI: 10,170.80Financing: Down Payment $ 32,475.00 25%Bank Loan Amount $ 97,425.00 75%Interest Rate5.50%Closing Cost $ 7,794.00 6%Loan Term (years)30Monthly Payment w/ ESCROWDebt Service / yr $ (6,638.02)Debt Service / mo $ (553.17) $ (1,063.00)As is your property you're looking to purchase is valued at 7.8% cap rate and will produce cash flow of $3500/ year.