This looks correct to me.

In this diff, you should change PhabricatorPhurlController->buildApplicationCrumbs() to use EditEngine to generate the "Create Thing" link. You can follow ManiphestController->buildApplicationCrumbs(). Without this change, the "Create URL" button won't automatically update to reflect the availability of multiple forms if users later define them.

In this diff, you should also change PhabricatorPhurlApplication->getRoutes() to use $this->getEditRoutePattern('edit/') to generate the edit route, instead of hard-coding edit/. You can look at PhabricatorPasteApplication for an example. You should be able to remove the create/ route after making this change. (It looks like Paste also has a defunct create/ route which could be safely removed). Without this change, stuff lik Edit URL → Configure Form → HTTP Parameters won't work properly.

In this or a future diff, you should change PhabricatorPhurlURLViewController to use EditEngine for commenting. D16222 has some extra stuff, but the changes to PhamePostViewController->buildCommentForm() in that change are generally reasonable as a model. Or just look at PhabricatorPasteViewController for a possibly-simpler example. After making this change, delete PhabricatorPhurlURLCommentController and the route for it (these will be fully handled by EditEngine, and no longer need a separate route). This change will enable the "Change Subscribers" and "Change Project Tags" actions when adding a comment, improve the draft code, and reduce the total amount of code in the codebase.