Erica has compiled a very extensive series of lectures about Copperplate calligraphy right here on the forum!:
https://theflourishforum.com/forum/index.php?board=20.0If you look for "flourishing" in the search box, you will also find a lot of discussions on this topic. A very good book is by Bill Hildebrandt: »Calligraphic Flourishing: A New Approach to Ancient Art«. It analyzes text flourishing types very systematically and across genres or styles, and encourages self-study (no instant gratification guaranteed, though!).
How long will you need to learn it? That depends a lot on how many time you’ll devote to it and how much is "translatable" from your Arabic calligraphy skill – maybe a lot, maybe not? As I never learned Arabic calligraphy, I can’t tell. But there are indeed European masters from the 16th century that claim that text flourishing comes from the Arabic, or was influenced by it at least!
For a more modern approach to ornamental flourishing, Schin Loong (also here in the forum) made a book about it flourishing: Schin Loong: »Calligraphic Drawing. A how-to guide and gallery exploring the art of the flourish«. It introduces you to figurative flourishing in a nonchalant and very hands-on way, and the basic rules are the same – wether for figurative or for text flourishing.
I hope that helps!