I have a question about brushing habits and gum health.

There are times when my gums bleed even though I think I brush my teeth thoroughly.
I'm wondering if it's because I brush my teeth too hard or if it's a gum problem.
I would also like to know if it is necessary to use dental floss or interdental brushes together.
I am wondering if gum bleeding can be reduced just by changing my brushing method.
I would like to know if the toothbrush replacement cycle also affects gum health.
I am also wondering if brushing alone is sufficient for proper care.