is this a good edh build?

For anyone who is looking, the general is Prime Speaker Zegana.  However, I would actually suggest changing your general to Vorel of the Hull Clade.  I actually have a deck that is very much up this same line and I find that Vorel is far more useful most of the time.  Being able to double the counters on just about anything can make a SERIOUS threat that many EDH players won't be able to deal with outside of spot removal (which is surprisingly less common than one might think in EDH... go figure).  Additionally, he's just HILARIOUS with Fathom Mage.

That being said, I think the wiggle room is going to be on the low end of your curve where things like Cloudfin Raptor and a few other creatures could likely be swapped for more productive cards.  I also see Laboratory Maniac, which I understand given how you can draw like mad off of Fathom Mage, but I don't know that I would be as worried about winning via the draw as much as I would be interested in keeping the load of cards in your hand (or recycle them from the yard).  So I'm thinking something like Venser's Journal could be good here.  Additionally, I would likely drop Diluvian Primordial for something like Conjurer's Closet which can work rather favorably with anything that has an ETB ability.

I can also say that in my experience, Fog or similar effects can be among the most powerful in the game, as a lot of players will hold back until they have a possible alpha strike.  To be able to drop a Fog and then kill them on your turn is obviously a nice play.  I could also see things like Sleep to be successful.

Keep tinkering... you're free to look at my build, but I'm not going to pretend that my build is ideal by any means.