Agreed. You don't have to hurry to get separated/divorced. Leave it for a while. Better yet, let it come from your husband. That way, you can always say that when you landed, you were of the opinion that although you had problems, you would work it out and in the end, it was your husband who pushed the separation / divorce. As long as there is nothing in writing proving otherwise, you are good.
You landing and a week later pushing a legal separation screams misrepresentation, that you knew you were about to legally separate and you decided to delay it just long enough to land.
When you don't have any processing going with CIC, there is absolutely no reason to report any changes in family status, change or address or anything else to them. Currently, you have no processing going on as you already landed. Therefore, you do not have to report a separation, divorce or anything else to them. You are however waiting for your PR card so you should keep your address updated until you get it.