Once again, I have to point out that this only changes the behavior of the "New Tiddler" button and does not fully address the OP goal ("the url field to be always visible from the start for all new records.")
There are at least 6 other ways to interactively create another tiddler:
* New Journal in the Sidebar
* New Image in the Sidebar
* New Here in the Tiddler Menu
* New Journal Here in the Tiddler Menu
* Follow a link to a missing tiddler, and then edit that tiddler
* Any 3rd-party plugin or hand-written custom wikitext that contains a $button using "tm-new-tiddler",
The only solution that handles all these cases (and any others that I haven't thought of at the moment) is to modify the EditTemplate as suggested by Brian Radspinner, with the small UI improvements suggested by me to remove the duplicate appearance of the "url" field, position it above the "create new field" interface in the tiddler editor, and enable use of $:/config/EditTemplateFields/Visibility/URL
respectfully,
-e