I don't think there should be a leader as well, but I do think that you need people that can do some QC'ing. I do have some advice for having this project not result in a "see how beautiful it is (but not really practical or useful)" project. The 4 categories that FF described are good divisions, but the categorizing of the current tiles and sprites Random made is not good. Most of the CG1 stuff I would have placed in CG2. I think there are some ground rules needed before things get put in CG1. This is so that you would end up with practical and usable tile and spritesheets. Mockups and sprites statues are by definition worthless.
I give this advice from a coder perspective, because it is really difficult for a coder to program in impractical graphics to a game.
Rules for tilesets
Technical guidelines
1) Each tile is 16 x 16 pixels I would preferably see it in 64x64 or 32x32, due to high resolution screens in size, although world objects like houses can be made by combining specific tiles.
2) There is 0 pixel horizontal and 0 pixel vertical separation between tiles, first tile starts at <0,0>
3) Transparency color is: Alpha = 255 (or 0), Red = 255 (or 0), Green = 0, Blue = 255 (or 0).
Practical guidelines:
1) Object tiles, like houses, trees, rocks, signs, etc., should be separated from surface tiles, like grass, ice, sand, etc.
2) Each tile should be made with layering. Meaning that tiles that need to be drawn over Link should not contain pixels from a tile that needs to be drawn under Link. Make those pixels transparent. Vice versa is the same.
3) Animated tiles need a complete animation before considered complete. Consider water, wateredge, flowers, waving canopies.
4) No mock-up images in tileset sheets. If showing mockups make a separate picture.
Rules for Spritesheets
NPC guidelines:
1) A NPC needs to be drawn in all directions (minimum of 3: down, left, up)I would love to see 8 directions, including the diagonal ones.
2) A NPC requires at least the following animations: standing and walking. It should be fully animated before considered complete. Other animations maybe requested but not needed to be considered complete.
3) When a NPC uses an object or something it is preferable to animate the object separate.
4) Effects that accompany some animations should be animated separate.
5) Yes on the shading, but keep the ground shadow separate.
Objects guidelines:
1) Even though most objects are static, when they contain a animation those should be fully animated. Take for example a pot. It mostly stands, but it can be throw and destroyed. Lit torches are by definition animated.
2) Effects of some animations and the ground shadow, should be kept separate.
Enemies guidelines:
1) An enemy needs to be drawn in all directions (minimum of 3: down, left, up)I would love to see 8 directions, including the diagonal ones.
2) An enemy requires the following animations: Standing, walking, attacking, hurting and dying.
3) When the enemy uses an object/weapon the weapon should be animated separate from the enemy.
4) Effects and the ground shadow should be kept separate from the enemy.
Link guidelines:
Because Link has a huge sprite sheet on its own you could add them by ability/weapon.
1) Link needs to be drawn in all directions (minimum of 3: down, left, up)I would love to see 8 directions, including the diagonal ones.
2) The ability needs to be fully animated for all stages of its ability. Make recognizable separations between the various stages. For example the stage of a bow: loading, releasing, standing, walking.
3) When the ability uses items/weapons animate them separate from Link.
4) Animate effects and ground shadow separate.
Well this my advice from a programmers perspective. If you keep to these rules for CG1 criteria it would facilitate game developers a lot, because they don't need to edit them to be of some use in their games.
Now to give some comments about this style. I really don't like it. The tiles are nice with the exception that the water is to purple, but when you look at the faces of those hylians they are stale and expressionless. I would suggest making everything in a larger resolution (also a nice idea due to high resolution screens). But most of all those faces show no emotion or any kind of expression, even MC and ALttP have more expression, variation and detail in the faces.