What are the best resources for learning Chinese with traditional characters?

If you already know simplified characters, it'll probably take just a couple of weeks to get used to reading traditional characters. If you're starting from scratch, the most common textbook series used in Taiwan are 視聼華語 and 當代中文. There're some other text around like 思想與社會, 今日台灣 and 從精讀到泛讀, but they're aimed at higher level students.

https://www.huayuworld.org/cluture-micro-video.php
many useful resources are here.

https://www.huayuworld.org/index.php
you can get whatever resource you need for your Mandarin learning from the above website.
Even download "textbooks" for different ages.

I learned traditional characters through the dictionary. Adjust your phone, and input into traditional characters as well.