Flex is going through the furloughed Flops pilots before they hire off the street. Not sure how long that will take but plenty of aircraft on order. I believe deliveries begin this fall. And yes they are getting more challengers. I believe the parent company is also picking up gulfstreams and globals. Sorry I don't have all the info.
I am in a hiring pool there and from what I can gather they are adding a ton of new bases. Just trying to find out which ones.