For example on a house I'm looking atCost- $310,000- 4BR, 2Bath DuplexMortgage (based on RedFins calculator)-  $2,008 / month, which includes taxes and insurance. 

In addition to the mortgage, property taxes, and insurance, the projected calculations are taking the following expenses into consideration (5% rate for vacancy, 5% for repairs/maintenance, 5% for CapEx, and 10% for property management; otherwise the income figures would be higher. 

I got my license for two reasons.  1) Just as @Jeremy Aldridge it gives insight on the entire process of the real estate transactions.  2) By law, having a license holds you to a higher standard in regards to disclosures you have to make which, if you are a shady business person, will hurt your profits.

Make sure the HOA doesn't have restrictions on vacation rentals. 30% is industry standard in most places.

There are often hidden costs--such as: engineer certification of the structure (depending on what the city requires) smoke damage to portions of the unit(s) that are "not affected" additional insurance during the rebuild, sealing the framing that has smoke, etc. 

I am talking about placing a factory built home on a permanent foundation with that home built to the same national standards as used for traditional stick built homes. 

Kansas City is one of the best cash flow markets in the country due to affordable prices, strong rents and reasonable property taxes and insurance.

The procedure is they have the contractor fill out 2 forms, they send an inspector to make sure the work is done (to some standard, I would guess), approve it, send me the money, and I send it to my contractor.

I'm the type of person who likes to standardize everything.

If you buy a home from a homeowner who is living in the home, is there a standard amount of time for them to be allowed to live there before vacating, while they look for another place to live and move there?