After you have replaced all drives in a zfs pool, you can expand it to the new size.

Windows? Seriously?

And just because it has not been mentioned yet: hardware raid does not guarantee data integrity by default.
Furthermore, your controller is a single point of failure. In case it goes down, there's a chance that it will take down all your data too.
You can't just stuff in another controller and expect everything to work again. Some suggest to keep an identical spare controller, even with the same firmware version.