You need a ruler to play your deck. This is most similar to MTG Commander. You either have a ruler in every player's pack, or you have a separate sub-cube just for rulers. In the old World of Warcraft TCG, every pack had a hero (equivalent to an FOW ruler). I like having a separate sub-cube just for the rulers because that cuts down the total number of rulers you will need to buy for the cube by a lot.
FOW is not issued as a draftable set. This is neither a good nor a bad thing. In an MTG set, a good 100 of the 249 cards in a large set are drafting cards, which are, in the vast majority of cases, cards that suck when put into a constructed deck (what in FOW is now just 'a deck'). I am not sure this matters for cube-making, but I know that the sets have very different distributions (will cost) in MTG sets that are draftable when compared to FOW sets. Actually, FOW sets are a lot more like the pre-draft MTG sets.
Many of the archetypes of FOW are not well-developed yet, and shouldn't be after only eleven 100 card sets and one 50 card set, plus maybe 50 more cards from other sources (starter decks, promos). That means you can't draft Elves, Cthulhus, Wererabbits, Card Soldiers, etc from your cube in sufficient numbers when picking them out of a draft pool. Once we have, say, 100 different Elves, Cthulhus, Wererabbits, etc, then we can build a tribal Cube with one tribe representing one color. Those drafts will then be a total blast because you can then draft cards that lord your tribe (give all Elves +200/+200 and so on), and cards that help a specific attribute (wind resonators get +200/+200 and so on).
A final aspect is power creep, which is normal in TCGs. It looks like resonators have gotten slightly stronger from one cluster to the next. I think I will build a Grimm cube first, buff it up with selected cards from later clusters, and then build a separate Alice cube with very few of the weaker resonators from Grimm. Balancing decks is a lot harder than it seems... this is the part of building a cube that is, IMHO, very difficult, and also a lot of fun.
This leaves a Cube designer with a few options this early in the game's history: pre-built decks, and goodstuff cards. The latter are cards that we know have performed well in tournaments. I am currently planning a Grimm cube, and it will have to be pre-built decks, and not goodstuff (cards that don't fit a specific archetype, and are just good on their own). After looking at all the commons and uncommons, I did not come up with enough numbers to build a Cube I knew could yield the same level of play I am used to with MTG Cubes. I am planning to build 10 to 12 decks, and then those decks are the ones that the players use. Maybe I will throw in a side-cube that each player can use to spice up the pre-built decks. I want each player to start off with a deck that plays well.
I will finish with an example: if you draft a Card Solider and a Wererabbit, you will want to play neither. I want the Cube to capture the flavor of many of the cards. Therefore, I will just build a Card Soldier deck that I buff up; and a Wererabbit deck that I buff up. Oh, and the pre-built decks will come with pre-built Stone decks.
