Stuffing of keyword on web page plays an important role in ranking of website, but always check the density of keyword
Using keywords effectively on your website will help you tell a better story to both your visitors and search engines, and it will help communicate what searches your website is relevant for…so that you can get more visitors from search engines.
Yes it does.
Title and H tags are important - because google will give more weightage if the KW is there.
Also try to include main KWs in the beginning.