I don't think that you absolutely have to do the kidney cleanse first, but if you want to do it that way, I would think a week would be fine. After you do the Liver Flush you can continue with the tea as an ongoing thing. As a matter of fact, thanks for reminding me - going to make a cup right now ;)
You need to grind fresh Celery seed for each cup, so you can buy a small jar of it in the spice aisle of the supermarket. It's actually sort of hard to grind the little buggers - they're hard to break open, like flax seeds are. But you have to grind them with a coffee grinder or a mortar and pestle to release the cleansing properties. Off to make a cup!