re: What's the focal length of a KH-12 reconnaissance satellite?
Doesn't seem to be available, but you could work it out if you assumed the telescope was almost identical to Hubble.
While you're thinking satellite imaging, there's a fascinating website run out of the University of Glasgow with lots of discussion of satellite imaging technology - many of the examples of improving surveillance imaging for Earth are identical to techniques being used on Mars to improve imaging there.
A starter document...