I generally use rounded spoonfuls as I find most recipes I start with are way under spiced. For garlic and ginger I almost always use much more than the recipe calls for. Once you get the hang of it, Indian cooking allows for a lot of improv. I do try to keep accurate records from batch to batch so I can continually improve.
As far as the optional lime and coconut, I do not use it. I think the lime juice may have a place in this recipe, but the tiny amount it called for seems almost insignificant. Maybe that's why I have never used it.