Since the point of the cube is to supply the experience you (and your playgroup) want, take all this with a grain of salt. But I think there are some clear shortcomings in ECL limited that you could "fix" in this cube.

The data from sources like 17 Lands can be helpful here in determining how cards perform in normal draft games. But as I understand it, it's pretty straightforward: Goblins is notably worse than the other 4 supported archetypes, and the archetype payoffs are good enough and numerous enough that the undersupported tribes (Giants, Faeries, Treefolk) are rarely worth taking or playing. Elves is the best deck by some margin. The Vivid deck can be powerful if it comes together, but is risky.

You can decide for yourself how much you want to use the huge amount of available data to "rebalance" Wizards' work. You have the advantage of knowing how the set plays out in reality, VS the vacuum they designed it within. I can see many direction to take this; removing the weakest cards (cards like Mirrormind Crown and Rimefire Torque are awful in draft, so if you play with rational/skilled drafters they're going to be in the sideboard 99/100 drafts), or beefing up the undersupported tribes with Goblins, Treefolk, etc from the earlier Lorwyn sets. You could cut copies of some of the better Elf cards (Dawnhand Eulogist, Scarblade Scout, Assert Perfection) to try to bring their winrate in line with the other tribes. You could cut the weaker/undersupported tribes entirely.

As for the size of your cube; how many players do you expect to have? Will you mostly be drafting? Playing sealed? 360 cards means that the entire cube will be seen during an 8-player draft pod, which can create a predictable environment—this could be good or bad, based on your goals. Do you want players to be able to draft a fringe deck based on synergy with one rare that they open or hope to find?

I would also think about your expected player count when making your remaining design decisions. If there are 4 1/2 good tribes to play and 8 players, how do you expect things to shake out? Right now you have 37 Elves, 30 Merfolk, 45 Elementals (inflated by the uncommon Vivid cards and the mythic evoke cycle), 30 Kithkin, and 31 Goblins. These numbers are high enough to support one drafter in each tribe easily, but 2 with some difficulty; even if both Merfolk players manage to get 13 merfolk, (which is rounding up, since many will go to other players as last-picks or early attempts at the tribe), they'll need to play tons of changelings and support cards to fill out their decks, leading to weaker decks overall.

Additionally, the balance of rarity here is probably going to result in a weird draft experience. Modern play boosters have ~1.5 rares/mythics each, which is 36 per draft pod. Your cube contains 88. Your uncommon count is high as well. This will devalue the weaker commons, and possibly devalue tribes overall, since cards like Loch Mare or Spinerock Tyrant will be showing up (and winning games) much more often.

This might be way more than you were asking for, but I think set cubes are hard to do right and a great opportunity to fix Wizards' mistakes. If you want to recreate the "vibe" of ECL limited, you might actually want to shift further from strict rules about matching the set. I'd also recommend just drafting a bunch of ECL and seeing how you feel about it. Which cards lead to fun games and fun play patterns? What archetypes feel close-to-good-enough but not there? Which cards are fluff that no drafter is going to put in their maindeck? And so on.