Hey Ioannis,
Is this possible creating new users?
Most of that is possible. The only thing in your list of requirements that isn't currently possible is the ability to limit users to viewing specific keys in the account. That is, there's not currently a per-key access control. You either give the user the ability to view key or don't give them that ability.
Everything else you listed is possible (they get their own web API key, you can limit specific abilities, etc.). We'll expand the "Adding users to manage your LimeLM account" article to make this clearer.