G'day,
Here's what I would do, involving a URL without the "#" :
Take a look at that TiddlyWiki instance.
You will see that upon startup, a startup tiddler checks for parameters in the URL.
The "action=createtid" parameter flags startup actions to create a new tiddler with the title specified and the template specified.
The TiddlyWiki is setup to show default tiddlers, including any tiddler tagged as "new_on_start", including the tiddler just created and any previously created tiddlers for which we haven't removed that tag.
This is a little different from what you had. We could also add some "post startup rendering" processing that sets all tiddlers tagged "new_on_start" in edit mode.
Cheers !