(The first link never brought up a picture for me)
Aiming high is never a bad thing, but trying to achieve a John Galliano dress shape starting from a Simplicity pattern is a bit naive. You need historical patterns, French Louis period stuff to pull that off. If you truly want that much volume in the dress, the structure underneath needs to be a lot more substantial than todays plastic boning hoops, you need baboo slats or steel or PVC pipe, something really rigid because that much fabric will wind up weighing a lot.
Bonus to seeking out the right patterns: the train will already be worked out for you.