Hello,
If i’m not interested at usaco contests and won’t participate, while learning from usaco guide, should i exclude usaco problems after each section/topic and do codforces/atcoder problems only or no?
You should not, as USACO problems still provide good practice, even if you won’t participate in the contests.
I think USACO problems are good, although they are longer/more time-consuming than CF/AC problems.