Some general musings here:

I think the biggest thing that jumps out in your cube is the percentage of multicolored cards (27%) you're running. When I was still figuring things out, my cube bloated to 800 cards (it's still big at 720, but multicolored cards "only" take 11,1% of the pie) because I wanted to run 10 card guilds. In reality this meant that players were hard pressed to find actual two-colored decks and this forced drafters into 3 colors simply because any size past 360 creates randomness. This means that one guild may be underrepresented while there are still tons of multicolored cards around which drives the player into 3 colors. Adding to this the 3 card shards/wedges and it's a done deal. So, point 2 in your post is a done deal.

Now, I say the above like it's a downside but if your attempt is to create a three-colored environment, then that's fine. If that's the case, I would also include 10-20 more lands to accomodate this because there's nothing worse than drafting 3 colors and not having lands to enable it. Refuges, Ravnica Karoos, Checklands - those are all options and the first two are very cheap and will do lots to help multicolored decks.

Second thing I notice is that green is missing the thing that defines and enables all things green: Mana dorks. You don't have to have them coming out the wazoo like yours truly but you do need some to give green that extra bit of oomph. If you find that 1 mana dorks are too powerful, there are several 2 mana options for you to choose from and having a handful of acceleration available will work wonders for all green decks - not to mention that you can choose to use dorks that produce mana in more than one color which in turn would support your multicolored environment. I would look here as the secondary stop in enabling your cube.

Last thing I would point to you is the analysis tool on cubetutor and particularly the curve charts tab. What you want for a smooth and playable environment is for each of the columns (colors) to form a curve with a distinct top to which the curve ascends and from which it descends with no bumps or potholes along the way. This is a thing each cube needs to address and if you find yourself with an overly high density of cards of a certain CMC, you might want to balance that out (looking at colorless 3 CMC slot in particular). Overall your curve does look fine, though, so aside from a couple of hitches you'll find with the analysis tool yourself you're pretty set in that regard.

Not a lot of cards jump out as being too good (Geist is pretty solid though, but then some bombs are warranted) for the cube so as far as balancing goes I think you'll just have to play it with your group and ask them to write down both the first picks and the last picks of each pack - that will start giving you an idea on what people value and what might warrant being cut down the road. (Don't cut something just because it's lastpicked once or twice if it fits to a deck though, but look for trends on cards that don't have a home and don't get picked.)

If you want something more specific, just ask.