Actually we use “很久以前” more frequent, whenever you want to express a long time ago( I think at least more than 10 years) you can use it.
As for "很早以前"，usually there are sentences before and after it. For example" 其实那件事是很早以前发生的=actually it hap pened a long time ago
“很早已经” in Chinese it's not a fixed sentence. we don‘t put 很早and 已经together（of course in a long sentence they can coexist but not “together”）
早 in Chinese usually means ’early‘。
久 in Chinese means a long period of time and ancient as well
both two words might have same meaning if they are added with other words：很早以前=很久以前（it depends on the meaning of the sentence）
a little tips：in Chinese there are a lot of situations that can't be understand，compared to many other languages Chinese tends to have less ’logical regulations‘，so just remember them in heart and don't spend too much time on “ why”（even Chinese don’t know why，hahaha）