The main keyword has 50k monthly searches and difficulty score based kwfinder is 40. The other keywords has 5k monthly keywords each one, and difficulty score is 30-35. I found a website which has 4 of those keywords in the same article and ranking #no1 in every keyword. He using these keywords on Headers and I found a lot of comments. Maybe if I will write 5x1000 words of the articles would be better using long tail keywords for the specific keywords? I really don't know what would be better for more traffic.
Why not? I read backlinko, Neil Patel articles which are 5k+ words articles, but interesting to read them. If the article has the keyword which you are searching for, maybe you are scrolling down the article until you find it and then you start reading the specific part.