Usually your phone should start just fine with an unlocked bootloader, if the flashing went well. That’s what I did, in order to check everything and take the time because of the anti-rollback feature. You should NOT lock your bootloader, before being sure your /e/os version’s security patch has the same (or newer date) your stock android version had.
There is a command to check, if it is safe to lock your bootloader. I’d have to look it up, or maybe someone here has it at hand.
Locking your bootloader will wipe your user data though, if you already use /e/os before doing so, and you will have to go through settings again.