E: Signature verification failed
E: error: 21
Is not itself a problem …
Install from ADB completed with status 2.
Installation aborted.
Is the point of failure … as if the recovery is wrong / non-functional in some way.
But now your image of e-recovery is e-recovery but why is it showing version 0.14 ?. [1]
I think I would be going back to reinstall recovery, and double checking all pre-install instructions at the same time. Ensure your battery level is at over 60%-70% at all times.
Was the phone newly delivered to you ? Had you had it online (and preferably with a SIM card) to have the phone make some connection with Samsung remote monitoring ? (I always think that instructions are written from the point of view that you have had the phone in normal use for a minimum of 7 days before attempting a Custom ROM). Hence the reason for
[1] Edit I am not a user of e-recovery, perhaps someone could chip in with current version numbering seen on their phone