In this market, with interest rates and prices at where they are, they're usually not viable (i.e. don't cash flow).

These were in the Myrtle Beach and North Myrtle Beach markets, but I believe this is a factor to consider in any market you're looking at. 

It sounds like a single family house where you will be living in the house(personal use).Therefore, you may not be getting the tax benefits you think you are.Consult an accountant.I am not sure why your sister would agree to this as well, she is losing $170,000 in this transaction and she faces the possibility of you increasing her rent.You also have to charge market rent or close to market rent or it is all deemed personal use.

In the future I would like to run Facebook and instagram ads in a market that guest from.

My custodian does not have a money market or similar sweep account to keep idle cash earning.

Quote from @Michael Calvey: Quote from @Sebastian Bennett: Can we re-name the reviews category: Rent to Retirement Marketing.

I look every day for off market houses to flip.

Welcome to the real estate hive.. are you open to exploring off-market listings through your network? 

Spring may be better but I was unable to sell a cheap house in October for 5% off of “market value” and only sold a $600k home in January by listing it for $580k and I still only got one offer. ($150k down, 5 year seller financing.) my point being you may get $20-$40k more in a year if you don’t need to sell. 

For your seller its an effective sales price of ask - 2% using your assumed $500,000 thats $490,000, a real good offer depending on your market.