Card level will be added to each card. Only player with same or higher level will be able to use the respective card. Non usable cards will be hidden and therefore not distracting the newcomer.
Well, if you're going to do it like this, then you can just set it as a (optional?) deck editor filter. And that still wouldn't prevent a high-level opponent from using them against you.
I don't think this is a good idea. If there is too much complexity, remove the complexity ._.