nice, i have a very similar deck. if you don't mind using older cards, you might want to look into manabond or Burgeoning.
Permalink
there's a couple cards i would suggest. mystic snake (it's a creature and a counterspell and goes well with Nulltread Gargantuan) and archmage ascension (you draw a lot of cards so it might help a little)
i am probably going to kick myself later for this, but i got some suggestions for ya: i would cut the frostwielder. there's a lot of cheaper cards that do basically the same thing. Wojek Embermage i think is more of a sidebar card for creature token decks and such. i would take the mill stuff out, maybe except the keening stone, just for an optional extra kill condition. some cards i would look into: razorfin hunter gelectrode Djinn Illuminatus erosion Pyromancer Ascension curiosity icefall raze roiling terrain seismic assult