The problem is the question is almost unanswerable. I wouldn't recommend iodine solely for heavy metals. There are other protocols specific for that, such as described by Andy Cutler. I take iodine for health. For that, a good target would be 100 mg a day. That could be 8 Iodoral 12.5 mg, 16 drops 5% Lugol's, or 150 mg SSKI (about 5 drops). Companion nutrients could include a minimum of 200 mcg selenomethionine, 3 grams vit C, 400 mg magnesium, and a good B complex. Variations abound.
Iodine will stir up heavy metals, and with enough selenium and vit C some of them (most?) will be ushered out. Very slowly. Iodine is very good at bromine detox, though, and a fondness for salt and water will help you through that stage.