@
phossler - I appreciate that you're making this book for yourself, and that you're probably using it as a means to learn about epub bookmaking. And on that; more power to your arm, sir.
However, IMCO - Artefacts such as borders, background colours and varying typefaces etc are very useful in instructional texts, and to a lesser extent in factual texts. But in fiction—no way Jose.
Well written fiction should facilitate/encourage the reader to use their own imagination, which includes such things as a letter writer's penmanship, and the paper they might use. Imposition of the bookmaker's visioning robs the reader of part of the joy of reading—exercising their own mental agility. What next? Put the jokes in Comic Sans MS
And seeing as you've gone to the effort of creating blockquote.handwritten, why not go the extra yard and get rid of the gap between the Compliment and Signature.
hint: your Compliment rightfully ends with a comma, so. . .
BR