Well, to get "ALL" the channels, you need FOUR dishes. Of course, you're not likely to be able to pick up 148 from Virginia, and it's almost totally a duplicate of 61.5, so only 3 dishes would be needed: 110/119/121, 105, 61.5.
Now, that being said, you might not need 105 or 121 or 61.5 - it depends on where your locals are, whether you want certain I'nat'l channels, and whether you qualify for CBS-HD.