The differences are in how they compute a "fingerprint".
Even if both applications use identical keys, the "human friendly" finger print they generate will be different.
1: What ssh server software do you hav installed on the Kindle?
Openssh or Dropbear? It looks like Openssh but I have to ask to be certain we are not wasting thread time.
That **should** have found it. But that may not be the correct name *or* the package you installed did not include it.
2: Yes. <name> is private, <name>.pub is public
Yes, the ssh server side key generation will put it in the correct place if you let it use default locations and names (which must be writable of course).
3: I don't have a clue. Show me the output of the command: mount and then maybe I can tell what you have mounted there.