Cube is a type of draft-based MtG. Essentially, one uses their old cards to create a new set. Typically, a Cube supports 8 players, but can be adjusted up (or down). Additionally, one can create other types of MtG games, such as a Commander Cube.
There are two basic ways to organize Cubes, but these are just general categories:
1. By mechanic
2. By theme
Another Cube was mechanic-based; my Make or Break Cube used cards that either created tokens or exiled cards/dealt damage.
The exact number of cards depends on a variety of factors, but for a basic 8-person Cube (360 cards), you want:
White: 60 cards
Blue: 60 cards
Black: 60 cards
Red: 60 cards
Green: 60 cards
Multi-color: 30 cards
Colorless: 30 cards
Repeats are okay, but not too many; no one wants to get stuck with a million Impetuous Sunchasers.
After creating the initial Cube, use CubeTutor to make sure the colors balance. The game isn’t very fun if one color is incredibly overpowered or if there is a Dimir card but no other black or blue cards.
Commander Cube is slightly different: for 8 people, you want a minimum of 960 cards, including non-basic lands and potential commanders. The trick is that ideally, there is just one copy of each card in the Cube. I’ve only played with 6 people at a time, so 960 worked out, but if you do think you’ll play with 8, you want about 1000 cards.
Ultimately, there are two really important things to keep in mind:
1. Cubes evolve and are rarely “right” the first time.
2. Cubes should be fun!