That's a tough one to answer - there are so many variables -
size of the orchestra
and so on and so on etc, etc....
My initial approach to a recording like this would be to start with a good but minimal orchestral mic'ing scenario. Perhaps XY with omni flanks - maybe blumlein with the same flanks (possibly without considering the group size.)
For the stage musicians - lav micing is passe and often considered quite an evil to the operatic musician. Boundary layers on the floor would be fine as would omni mics on some type of acoustic panel to minimize close reflections.
As for the phasing or the movement from one side to the other, you're pretty much on your own on that one. You could always run everything mono on the stage and leave the orchestra stereo which would minimize the movement, but at the same time make the singers appear as though they are all singing from the same point in space.
My take is, record it as is. If there's timing issues or movement issues, it's just a fact of life. Many of the finest produced opera discs are just that - produced. Singers standing at finite points never "physically acting" just singing. Many other great recordings of operatic works take the complete opposite approach and simply display what the audience would hear - movement and life.
Hope this helps...