Thanks for the reply.
I'd created much the same thing... I think the bit that was missing (until I just spotted it) for me is the Keyboard Options and the ability to have the Text input pop-up check-spelling, and offer sugguestions.
I've enabled these and it makes it much more usable.
It's still perhaps not as slick as if the cursor were in the filename right away, or if the first line of the document body could form the name. But it's better.
Perhaps what I'm really after just isn't do-able.