tarot cards, which card follows 'the tower"...before shuffle?

The star. Meaning having hope, after the tower, or destruction/shake up. The star, calmer times, time to reflect, picking up the pieces from the tower, in which the lightening brought.

The Star is the 17th card in the Major Arcana.

(Tower being the 16th.)

I don't think you need to stack your deck before shuffling, unless you think the question is really important and you think the sorting helps, and you'll shuffle intensely afterwards.

16--the tower

17--the star, as stated above.

I repeat, I don't think you need to sort your cards before shuffling. To study them, I'd expect you to. But not before casting.