Hi RP, Your query elicited some good advice from two excellent turners,
and you obviously are no slouch either. Beginners should heed their
advice and follow your plan. David's caution re not letting the blank's
size dictate the form should be emphasized. This advice is hard to
follow with expensive or even 'road kill' wood. As with other turning
admonitions like the bother of persistent resharpening of tools, it is
important for turning 'pretty'.
I've made a lot of ordinary NIP pieces by trying to get the largest
possible instead of wasting (a misnomer) wood by adjusting to get a
smaller but nicer piece.

Remember the potential toxicity for flora & fauna by the walnut
shavings. Also, for security use a face plate instead of a scroll chuck.
No doubt about Jim's advice that you should back off from vibration
speed when roughing big blanks. I might mention that going a little
beyond vibration speed on a _balanced blank can often safely smooth
things out. Please share the story of your life with big bowls. Arch

Fortiter,