when I build a sald deck i usually go 3 colors with 18 land usually 8 in the strong color 6 in the second and 4 in the off splash.
2 colors I go 9 and 8 17 land
4 colors 7 5 3 3 or 8 5 3 2 18 land
5 colors 7 5 3 2 2 19 land
how do you guys set up your land?
I usually go with 16 creatures and 6 cool spells almost always creature removal and bounce fill those slots.
how do you set up a sealed deck?
it really depends.
In masques block the number was often 16-17 land
and about 16-17 creatures, but in Invasion block, the high amount of removal and tons of coloured mana symbols means you usually need 17-18 land, and you can often get away with 13-15 creatures ( I try hard for 15, but I've seen successful sealed decks with as few as 12).
Nevyn is right. In invasion I go 18 land with 3 colors, 17 with 2, and I almost never play more then 3.
I usually don't worry about creatures because I usually end up with a lot of removal, and a removal spell can replace a creature just fine. I usually play 12-14 creatures and 8-10 non creature cards, and I do great. If you only have a couple removal spells, try not to play any cards that aren't creatures or those removal spells and over run your opponent. Other than that, just sit back and let the deck play itself.
You can go down to as few as 13-14 creatures if you have strong removal, or a lot of utility like Probe with kicker and Fact or Fiction.
I have played with as few as eleven creatures in Invasion and lots of removal and discard. Discard is underated by many and as good as removal. Give me Clouds and I'll grab 'em.
I prefer 12-15 cretures and around 17 land. But you need to be a bit flexible in Invasion draft. Often people will start drafting a color halfway through that you thought was yours. Some colors have weaker creatures as well so this might alter the numbers a bit.