1. Do you think it is best to avoid errors in class? I don't think the best option in class is to avoid errors, I do very much agree in what the unit says: errors are basic for the learning process of every student.
2. Which of the ideas (in exercise 5) have you tried yourself? Most of the times, I use student's mistakes as warm up activities to introduce a grammar point, a writing activity etc...
3. Do you believe it is important not to interrupt students when they are speaking in order to draw attention to their errors? Yes, I do believe it. I think speaking is something always hard for them and I don't think we help them if we interrup them in order to correct them. But, we can suggest a group correction for example: ask other students to keep a written list of his/her mistakes and then, at the end, they can explain them or correct them.
4. How do you help learners to see that making mistakes can be a positive thing? I think the best way to prove them that making mistakes is not a terrible thing is by not taking them into account in your marks. I always tell them that I would never evaluate them according to their correctness in activities done in class to practice. Then, I convince them.
It's obvious mistakes must be part of the learning process and for this reason, we 'need' them in classes.