>Each curation member has his Curation Reputation Tag. The more upvotes the posts - he curated first or from the first - gets - plus his continuous curation - the more his reputation grows. A member with a higher reputation is like a lot voters with lower reputations. 

This is actually a problem with the current curation system.   People begin to dogpile popular people.   It is part of why the curation system is broken now.  People who pick the topics that will do well.   Of course they will do well if the curators keep always picking the same people.   It is a sure fire reward, but it is crap for the platform.

>no curation bots should be allowed

No way to detect them so you can't really make them not allowed.   All they are is code to act like people.   So any detection attempts will also flag people and once learned can be circumvented.   So you cannot eliminate bots.   That is why they haven't been.

>Downvoting should be made by at least 3 curators with a minimum curation reputation.

This can be easily gamed.   By the method you have defined curation reputation can be easily farmed.

The current reputation system is the only thing that seems to have a limited effect against abusers.   It is not perfect.    Yet to gain reputation you can only gain in reputation when someone higher reputation than you up votes you.   You can only lose reputation when someone higher reputation than you down votes you.

As you climb in reputation the advancement becomes slower and slower as there are fewer people above you to help you increase.