fastboot devices If you see a serial number, you are connected. Navigate to the folder where you saved the crDroid-recovery.img.full file.
fastboot flash recovery crDroid-recovery.img.full Do not boot into the system yet, or the stock ROM may overwrite your new recovery.
A: Yes. Once crDroid is installed, go to Settings → System → Updater. Download the OTA. When it asks to reboot, it automatically uses the existing crDroid recovery to install the update silently. You don't need to manually flash the .img again.