So from my understanding kunyomi is used for single kanji understanding and onyomi mostly for kanji that are combined into words. So I guess it is better to put more focus on onyomi to go smoother through reading material? Which did you learn first?
Two other question’s
Anyone has a list for all kanji seperated into grade levels.
What is the best extension to use to filter out a kanji from a website. Raikichun?
Whole that can be a case often it is definitely not a hard-and-fast rule as there are plenty of exceptions. You learn the kanji 秒 in level 11 and the word 秒 uses an onyomi reading. Same with 一, 二, 三, etc.
No because your original premise is flawed. Both single kanji or multi-kanji words can be either. There is no good reason to only learn one to the exclusion of the other.
It’s better to focus on learning vocabulary and you’ll learn the kanji readings by extension. For example, the letter C in English sometimes has a K-sound and sometimes has an S-sound, but you don’t just sit down and practice the sounds. No, you learn that “cat” has the K-sound, “ceiling” has the S-sound, and “circle” has both. It’s the same with Japanese - native Japanese students don’t focus on learning the letters in isolation, they learn words.