"If starting new creature, is it okay for a person to have more than one login name to monastery?"

As far as I can see, there's nothing to stop it. I don't think there is any way to garrantee this could/would be detected, so it becomes more of a personal issue.

How do you want to spend your time at the Monastery? As one identity or as several? Do you want to remember "who you are" before using the CB? Before posting a node? Or do you just want to be yourself?

"Does this fit to moral (and ethical:) rules?"

Whos moral? It's your own moral. Live by your own ethics and feel as good as it makes you.
Personaly I think it's not so much a question of if you should have multiple logins, but more of how you would use potential multiple logins.

"(not to mention that 100% sure those creatures will ++ each others)"

Again, it's very much up to your own moral and ethic. What about people who know each other. Do they ++ each other? It's up to everyones moral. And also very much up to how much you value the XP.

How would you feel to become a Saint, knowing that your best (?) friend has upvoted even your most silly nodes?
How would you feel to become a Saint, knowing that you upvoted all your postings yourself, using a second (or third?) login? Your call. But think before acting. Your consious will guide you.