Hello,
We just hook into the WooCommerce my-account page for vendor registration.
If you would like to use all of these fields (either custom added or … are you using buddypress??) You could then direct your registered users to the pro dashboard after they have registered to sign up to become a vendor. Rather than trying to edit the my-account registration.
Does that make sense?
You can then require the fields for the vendor application by using the filters to require the fields.. this is an example of how to make a field required:
https://gist.github.com/fervous/badc146c8967781e36e154b68a4609e5