Do I have to keep taking tutorial, training and practice tasks?

Tutorials help you learn about tasks and give you access to Qualifiers. You should take all Tutorials at least once.

Tutorial and Practice Tasks will always be on your task list, and after you take them the first time, you can take them more times if you'd like.

However (and this is important): you don't need to keep taking them just because they're on your task list! They're there for extra practice and to reinforce what we're looking for in a skill, but you only need to take them once. We do not track how many times you take these tasks. We will not assign more tasks based on training tasks. 

You can also hide them from your iOS task list.