Generally you turn the necks one time, before any other operations except expanding the neck with a mandrel just enough to fit over the pilot of the neck turning tool.
Afterwards, depending on the size of the expander/pilot combination you're using, you may need to size the neck some to get sufficient neck tension to hold the bullet for the initial firing.
I have used the Sinclair expanding Mandrel and turning mandrel system with great results and no problems with it. I combine it with a battery screw diver for ease of use.
I use a 21st Century turner, I don't know if it's the best or worst, it's the only one I have ever used, but it simply works, very easy to set up, comfortable in the hand, adjustments are easy and highly repeatable.
I use the 21st century turner. It works really well for me. I use a 1/2" drill on low speed and just drop the case in the chuck. Really fast and repeatable. I wait until I have a couple of firings on new brass before I turn them so I can get really consistent trim length on everything without being too short.