This deck would be even better if you add the tron lands: Urza's Tower, Urza's Mine, and Urza's Power Plant. Also, some cards that would be AMAZING in this deck are Mindslaver and Torrential Gearhulk

To be perfectly honest I don't think any of those cards add anything to this deck. I already have more mana I will ever need, the only instant/sorcery cards that will be in my graveyard are Diabolic Revelation and Mind Spring so the Torrential Gearhulk won't help, and Mindslaver only works once.

Voyaging Satyr is another untap land ramp creature that you could play, it would speed up your deck a lot if you added some more enchant land ramp like Fertile Ground too. They're cheaper and probably better (in terms of speed) than Elvish Harbinger and Kodama's Reach.

Elvish Harbinger is used as a tutor to get more Arbor Elf's. Also it allows me to diversify my mana sources. I play Elvish Harbinger, Karametra's Acolyte, and Chromatic Lantern so that my opponents cant just destroy my land/enchants and completely screw me over. I also like to have Kodama's Reach as a way of cycling more of the lands out of the deck, so you are more likely to draw something useful. Voyaging Satyr is a good card, but I don't use it because I would have to swap out something else or go above 60 cards. Same goes for Fertile Ground. Thanks for the feed back.