About your second point: I also think Metraton would indeed go first after William to see if Kevin is with him. I’m sure Kevin probably knows that, and that’s why he told William he didn’t plan to stay long with Michael that’s a shame because I reeeeeeally like the idea of William, Isaac and Mathers having to hide two archangels and William having to interact with Michael ;p
I can only hope Mathers’ magic shield is powerful so they all can stay for a few Pillars without being bothered by Heaven but – unless Mathers is revealed to be a powerful god/angel/demon or Jesus – his shield probably can’t hold back Metatron longer.