cook brisket thrusday for saturday?

Mmmm... Absolutely ! It will be to plotz for!

Agreed about the flavor improving. Assuming you're doing a traditional brisket pot roast for Passover, the other benefit is that the fat in the braising liquid will rise to the top and harden in the fridge - making it easy to remove as much as you want. I'd store the meat in the sauce. The cold brisket will slice easier too.

Cooking a day (or two) ahead is SOP for many cooks. Refrigerate sauce separately from meat. Before reheating: Defat liquid, slice meat, fan out in a baking dish, pour sauce over top, cover and reheat in relatively low oven.

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I agree with mbergner on this. It improves with a few days in the fridge.

It will keep up to a week (or more). Like a good stew, it is actually better the next day or two. Wrap well so it does not dry out.