Personally, I find the text on the tombstone item to be a bit too close to the top, especially with larger text sizes and with some of the variants. It would be nice if we could adjust the distance between the text and the top of the headstone, as well as the distance between the header text and subtext.
Additionally, although the text input works fine for the English-speaking playerbase, the fonts the gravestone uses lack support for non-English characters. Adding in a font like Noto Serif/Noto Sans (which supports a large amount of languages) seems like a good idea, particularly since the in-game chat and notebooks (minus the text on the book) already support these characters.
You can use Enter before a new line (or an empty one with just a space in it) to move the text further down.
I’m surprised it doesn’t include non-english support, but that may have to do with the typefaces they chose.
Since the Gravestone is essentially the prototype for normal sign items (Halloween is usually the time when they try new ideas like this) these issues may be fixed when the normal sign items are made.