1st is good. 2nd is more natural as: My friend was fond of working out every night. It’s a little odd to use ‘fond’ to describe a habit, especially if you are emphasizing how consistent he was. My friend worked out every night. Steven worked out nightly. My friend Steven worked out every single night. My friend Steven was fond of working out. He did it every night. (The fondness is usually for the activity, not the timing)

Very nearly perfect. In the second sentence you need to change “workout” to “working out”.