I am a builder in the area and you can make at least twice as much depending on the area of Charleston you are in and the value of the homes in the area.  

If you are asking what the cost of rehab is, well that depends on the condition.

Refinance raises the payments potentially & the higher interest rate may improve your tax write offs depending on your bracket.  

My wife works with a lot of investors as an agent (Florida), but she's personally built or flipped scores of homes, she has a construction background with an actual degree in the field, and she's spent years honing her craft.

Depends on if you tenant still wants to live there after its repaired.Also congrats on a brand new home, insurance will likely build a new one depends on how severe the damage is.

Below is a 5 year chart of best, average and worst outcomes for home prices (depending on who you are of course) from Fannie Mae, our more “conservative” price forecaster.

Depending on your personal finances, shopping for a triplex or quadplex may require the existing market rents to pass a self sufficiency test, to ensure that you will be able to pay the note.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

In the buy and hold situation, depending on what you buy it for, the expenses of owning/taking care of it, and how much you can rent it for, you could have some cash flow each month and have a second property that appreciates each year. 

Depending on the loan product used - to purchase a non owner occupied investment property you will need a 15-20% down payment plus closing costs.