Sherlock.Holmes: what is the difference between nodekey file and keys in keystore folder?
Also can we mine using the same public key on multiple machines?
nodekey is the node ID, which represents a locally running instance.
keystore is your wallet file and must be stored properly, preferably offline.
The same address can be set on different machines, which does not affect the mining probability. We have previously imagined setting different addresses on different machines, but in a decentralized environment, this setting is meaningless.