In addition, here are some more things that you might want to customize.

HTML vs Text email

During customer signup, there is an option asking them whether they want HTML newsletter or Text newsletter. Actually, that choice affects not only newsletters, but all the other emails such as "Welcome Email", "Order Confirmation", etc. So you might want to change the wording to say "Do you want to receive email in HTML format or Text format?". The choice is defaulted to Text by ZenCart. But you can alter the code if you like.