Halimar Wavewatch is probably one of the better mana sinks other than the absurd Sprout Swarm. It's done considerably well in our cube. I was really hoping they might make Magma Jet a common but i guess that would have been pretty amazing in draft, dang.
15 is way too much, IMO. Even 14 has been too much. The normal boosters have way less playables and in my experience, you will always see similar decks with the same cards played if the players have too much, to choose. With 2 or 3 players we normally use the Winchester draft system. With 4+, we play 4x10. That's a pool of 40 cards per player, exactly 1/10 of my cube and it's fairer than 3x13 (39 cards), because it goes 2 times in one direction and 2 times in the other direction.
I can only recommend 4x10 boosters.
The difference between 3x15 and 4x10 with 4 players is a difference of 5% of your total cube, an increase from 40% to 45% (not even half of your total cube present in one draft.) I don't see how that 5% margin could make it from seeing diverse decks to the same old decks every draft. If anything, more cards present = more possibilities but once again...5%. I'm not saying its not worth running a different pack size but I think the thought process goes in the other direction. Smaller packs and less total cards is likely to promote tighter goodstuff.dec building in which people are trying to get as many quality cards as possible rather than taking fringe cards in hopes for finding its pair to create a synergistic deck.
I will say that I am a fan of having more packs and fewer cards per pack ( I run 5x9) with 4 people because it makes it not so awkward seeing the same pack go around 3 times as it would with 3x15 with 4 people.
I've always been pretty tempted to play with rebels because they're a bit of a pet archetype for me because I love the fact that they add both versatility and card advantage to white but they're just aren't enough of them to work in my cube. I run a 360 cube that is most often only drafted by 2 or 4 players. If I ever trimmed my cube down (i've even considered going down to 180 ><), I would probably be very tempted to include the better rebels but they won't show up in my pools enough seeing as sometimes I only see 1/4 of the cube in one draft. Slivers are in an even worse spot than rebels IMO. They not only need a critical mass (even more so than rebels) but also need duplicates in the form of Muscle and Predatory sliver which we can't really cater to in cube.
I could see it being good with a little support and it's probably the best card I mentioned but my cube doesn't come to stalled board states very often. I think I might run a little too much removal but there aren't usually more than 4-5 creatures on the board at a time barring something like Sprout Swarm.
EDIT: This post is not in anyway meant to criticize your cube because I think it's cool that you have built a unique/themed cube that i'm certain is fun to play but simply a retort to the fact that the mentioned cards are at the same power level as other cards offered at 450 or even 540.
I'm with Izor on this one. My drafts aren't usually very large and often only 1/2 of my cube is seen at one time. Putting in cards that are only good with certain other cards seems silly in such circumstances. The only card mentioned thus far to even interest me has been Goblin Matron since running cards like Skirk Commando and Nameless Inversion are perfectly fine for power level. A 1/1 is still pretty meh tho.
EDIT: If you think Coursers arent worth running you're fooling yourself ><
Kird Ape is a R/G card because R/G fits into the guild system. Wild Nacatl doesn't because 99% of cubes don't support a tri-color section. It can be just as much a G/W card as a G/R. Kird Ape is exclusively G/R because it blows as just R. There's nothing consistent about that filing.