Yes, 10 car and 5 car operation for the full Trent work. The 12 car working from Crewe from December is in anticipation of this.The LNWR ones are based at Bletchley so keeping them on MKC/Tring makes sense. The 350/2s were originally ordered for these routes (explains the 3+2 seating) and 37 350/2s to 36 730s isn't a coincidence.
LNWR unsuprisingly want their new trains on their longest (IMO their flagship) route, do London to Crewe gets mentioned though I'm doubtful it will get much 730 operation.