Send them a contract, and ensure that it's a legally enforceable and valid contract. 

When I started to build my list, there was a notice on the page that data from Kansas was excluded.How are other investors in Kansas building these lists given this limitation?

Generally, the County has a commission that put together a few data to find the assessed value of all properties and, upon that value, applies a mileage rate (a percentage).

This is current data and it just is what it is:Among the 53 metro areas analyzed in the report with at least 1 million people, those with the highest share of completed flips sold to all-cash buyers - often other real estate investors - in 2018 were Detroit, Michigan (48.8 percent); Birmingham, Alabama (42.4 percent); Jacksonville, Florida (39.8 percent); Miami, Florida (38.3 percent); and Buffalo, New York (38.0 percent).Completed home flips in 2018 yielded an average gross profit of $65,000 (difference between median purchase price and median flipped sale price), down 3 percent from an average gross flipping profit of $66,900 in 2017.

My free advice is to ensure you have someone escrow the sale and check provenance of their title; that is, don't send your money to the seller hoping they will send you a valid deed back later. 

Is the two weeks based on the inspection period(i think) how do I ensure that If i do not find an end buyer within the two week, I can get out of my offer?

Time, Control, Speed, Access to data, Commissions on your buys, Paying less commissions on your sells...The list goes on.

https://overflow.solutions/demographic-data/who-is-moving-to-each-state/

Another big aspect that will help you avoid vacancy would be to ensure you are renting your property at a reasonable rate, which you can determine by looking at what is renting or has been rented around your property!

And then you can start implementing measures to ensure your tenants pay you and don't damage your property.Good luck!