1. 3 grams of fat are needed for each fully balanced Zone block.
2. No, don't multiply them by two. Then block system is designed such the half the fat (1.5g) is in the low fat proten block, and the other half (1.5G) in the added monounsaturated fat block, for a total of 3g fat.
If you choose a fat free protein like egg whites, then double the amount of monounsaturated fat blocks you add, becdause the protein block is missing the 1.5 g fat it is presumed to contain.
3. It's not necessary to count a cup of two of raw spinach, since it is a negligible amount of carb.
4. You don't substitute fat for carb. You may be thinking of the temporary drop a carb adjustment to jump start a weigth loss plateau. Some people add a few extra fat blocks when they do this adjustment, others don't.