What's up with Number One? She sits at what eventually becomes Sulu's helm position
Yes, but my take is that Number One is also sitting at what will one day become Data's position too. Number One is sitting at "Ops." On the Enterprise Dee, owing to it's size, the ship has a dedicated First Officer with no other duties besides that position, the Second Officer handles ops duties. The Pike Enterprise is much smaller, so the First Officer also is ops. Lt. Tyler is the helmsman (and navigator).
Given Voyagers size, with a 150 member crew, the 13 department heads should be reporting to Chakotay. If they are instead reporting to Tuvok, it might be in his capacity as the ship's Second Officer, and not specifically to him as the security chief.