GB,
The used airliner market is the place to get additional refuelers - if there's a need.
No, and yes.
AFAIK, the challenge with the former is finding enough low time aircraft in a common configuration that will stand conversion and provide the capability the USAF is looking for.
It's not quite the problem the RAF ran into with the VC-10s (ie, operating a unique fleet of aircraft) but it's still likely to be a nightmare.
S41