Solid build although I would consider replacing the
Nissa's Renewal with more
Fumigate - it seems unlikely that you will need more land in a hurry by the time you have 6.
Fumigate seems more useful than 7 life when you are out of
fog and facing down an army.
Also, have you considered
Gruesome Slaughter? Since the creatures created off Metallurgic Summons are colourless,
Gruesome Slaughter allows you to tap them to deal direct damage to your opponent (plus it gives you a 6/6 summon which is neat).