What is the way to overcome desperate thoughts about the torment of the grave and Hell, and the feeling that acts of worship are worthless compared to the Companions and the Successors?

A believer should be fearful and hopeful, combining the fear of Allah's punishment with hope in His vast mercy, so that fear does not lead to despair. What helps achieve hope is to recall Allah's mercy, the immensity of His generosity and bounty, and to reflect on His beautiful names and sublime attributes, and His blessings that indicate His mercy. Similarly, recalling the lives and stories of the righteous is a good thing that encourages emulating them, even if falling short of them is inevitable, for whoever walks their path will quickly catch up with them.