Always have some backup emergency food as small town America is slowly dying off unfortunately and therefore the grocery that was open last month may have finally closed. The ACA maps are good and show the services and the addendum are kept fairly up to date.
Yes, you will meet other riders going your direction but it will probably only be for a few days before one of you takes a break or keeps going. It will happen but not every day.
Two to three bottles is most common. You are in Kansas and you know what summers can be like. You can plug in several places along the way (cafes, CGs, CS, etc.) but consider getting a "power pack" (external battery). Also, just keep it turn off and check it periodically 4-5 times a day and the battery will last a lot longer.
Remember, tens of thousands have done this over the history of the route so if tens of thousands could do it, chances are you can too. On the plus side, we don't have to educate you/reduce your stress about tornadoes .
Go over to CrazyGuyOnABike.com and review the vast bank of journals on the TransAm. Almost any question you have will be answered after reading a few of them.