Yes, a 3' clearance is fine between the vanity and the shower. FWIW, I prefer a toilet closet for privacy when more than one person is in the bathroom at the same time. And I see no issues with the layout of the powder room. That said, I'm not wild about the idea of having to walk through the bathroom to get to the walk-in closet. If it were me, I'd swap the locations of the bath and closet, then turn the big walk-in into two reach-ins (his/hers) with one closet on either side of the walkway to the bathroom. You could put in either sliding closet doors or bi-fold closet doors to save hallway space.