Hey Michael - I've watched a few dozen putting videos looking for good drills to setup at home and this is by far the best. Instant subscriber 🤗 I'm going to have a crack at combining all three drills into one.
String line is a great tip, you can see when you're not taking the putter back in straight line, and hitting the ball when the face is not square. Didn't take long to rectify that mistake. Just need to practice and more practice.